I have not went through and verified everything here, so some of this may be slightly off, but it still gives a great impression of what 6th edition is all about.
via Zion over at Heresy Online
General
Premeasuring is now in.
Night Fighting can happen in any game (on a 4+) and if rolled will continue until the roll is failed at the start of a turn (Night Fighting limits weapon's max range to 36" with anything over 24" counting as "Shrouded" and getting a 2+ Cover
Save. Any model over 12" away counts as having the Stealth USR).
Turn Order remains the same (Move->Shoot->Assault). No psychic phase.
Jet Packs give Relentless and 2D6" movement in the Assault Phase if not Assaulting.
Squad Leaders (Sister Superiors, Space Marine Sergeants, Eldar Exarchs, ect) count as Characters and can accept challenges and benefit from the "Look Out Sir!" rule on a 4+.
Area Terrain grants a +2 Cover Save(?)
Reserve Rolls changed: Turn 2 = 3+, Turn 3 = 2+, Turn 4 = Automatic
Random Game Lengths are still in.
USRs
Snap Fire - Fire weapons you wouldn't normally be able to fire at BS1 (heavy weapons, sponsons on a tank that has moved and fired it's main weapon....more information will be available on the exact details upon the release of the rulebook). Blast weapons may not snap fire.
Acute Senses - Reroll Outflank.
Night Vision - Ignore Night Fighting.
Stealth - No Change.
Rage - +2 Attacks on the charge, no movement penalties.
Fear - (Currently Daemons of Chaos only but that is pending FAQ) Same as Fantasy. Leadership test to avoid being WS1. Units that are Fearless or have "And They Shall Know No Fear" are immune.
Jink - Currently mentioned as a rule for Fast Skimmer and Jetbikes. Gives a 5+ Cover Save if the model moves at all, and a 4+ if it went flat out.
Fleet - Allows you to reroll the run roll or the charge roll during a turn. No longer allows you to run AND assault in the same turn (as that'd give a unit with this rule a 24" threat bubble under the new rules).
Hammer of Wrath - Single attack at I10, hitting at strength (no word of it auto-hits or if you have to roll to hit). Jump Infantry is said to have it, and the recent White Dwarf seems to imply Dreadnoughts may have it too.
Zoom - a Flyer USR that keeps the flyer from ramming, tank shocking, being rammed, being tank shocked, must move 18" if at all possible, may turn up to 90* before moving, can move upwards to 36". It may still fire 4 weapons when moving at these speeds. If the flyer ends up moving off the table due to the Zoom rule it may roll to come back on the next turn.
Sky Fire - Allows you to shoot at Flyers without penalties.
Vector Strike - Flying Monstrous Creatures can attack models they fly over inflicting D3+1 hits at strength.
Relentless - No Change.
Fearless - Possible change to assaults: Fearless may no longer cause casualties from losing combat. Fearless Units can't elect to break from combat if they're locked in combat against a unit/model they can't hurt.
Counter Attack - No Change.
Feel no Pain - Now 5+ and is only prevented by Instant Death.
Instant Death - No Change.
Calvary - No movement penalties for difficult terrain, however it is now dangerous terrain (no word if this applies to the change to initiative for assaulting through cover though).
Beasts - Ignore all penalties for moving through terrain (to include assaulting).
Smash - Monstrous Creatures can use this to halve the number of attacks they make on a vehicle to strike at double strength (rumored that it may also let you reroll the penetration result as well).
Preferred Enemy - Reroll all 1s for shooting and close combat (both to hit and to wound).
Furious Charge - +1S, No I bonus
Slow and Purposeful - Move 6", Can Not Run
Skilled Rider - +1 to Cover Save
Rending - AP2 on the roll of a 6, +D3 to armor penetration roll versus Vehicles (also on the roll of a 6)
Weapons
All Close Combat weapons now have an AP value (ranging from - to 1)
Power Weapons now have types with different rules and stats. Most commonly mentioned are the Power Sword (AP3, MAY give a 5++ Invulnerable Save in Close Combat) and the Power Axe (+1S, AP2, Unwieldy). Other types like spears have been mentioned too. If the type of Power Weapon is not mentioned in the book or the FAQ/Errata then the type will be determined by what the model is actively equipped with.
New Weapon USR(s): Unwieldy - Weapon strikes at I1; Rapid Fire - Always get 1 shot to full range or 2 shots at half range. Still can't assault after Rapid Firing; Salvo - Full number of shots at max range when stationary, 1/2 number of total shots at half range if moved.
List of the new Power Weapons as follows:
Powersword: AP3
Poweraxe: +1S, AP2, I1
Powerfist: 2xS, AP2, I1
Chainfist: 2xS, AP2, I1, 2D6 vs. armor
Powermaul: +2S, AP4
Powerlance: +1S & AP3 on the charge, AP4 otherwise
Lightning Claws: S User, AP3, Melee, Shred, Specialist Weapon
Forceweapon: AP3
Force Sword S User, AP3, Melee, Force
Force Axe S +1, AP2, Melee, Force, Unwieldy
Force stave S +2, AP4, Melee, Concussive, Force
Unusual Force Weapons - Force Weapons with special rules are AP3 and use the special rules in their codex (this means you Grey Knights)
Pistols don't add any additional bonuses in combat (may still retain bonus attack for being paired with a CCW though)
Sniper Weapons still wound on 4+, have pinning and rending.
Weapons that don't roll to hit (like the the Monolith Portal) can not be snap-fired. This does not affect Flamer Templates (at least the ones in squads, vehicles are unspecified).
Plasma's "Get's Hot!" rule now effects vehicles. If the Plasma weapon rolls a 1, a second die is rolled. On 1-3 the vehicle takes a Glancing Hit.
Poisoned Weapons wound on a fixed number unless a lower number would be needed. No more rerolls.
Close Combat
Assaults are no longer static charges. 2d6" assault range for all models.
Different unit types have different assault ranges. The main rulebook has a table for these
Multi-Assault (assaulting more than one unit with a single unit) no longer gives bonus attacks.
Assaulting Through Cover - Roll 3D6 and discard the highest. Strike at I1 unless you have Assault Grenades.
Overwatch - When charged units able to shoot may do so using the Snap Fire rules. Templates hit d3 times, blast weapons may not be fired. This can only be done once per unit per turn.
No Parry Saves.
Shooting
Shooting now only works against models the unit can see, with the enemy unit taking saves from closest to furthest, only pulling casualties as models fail their saves. This will likely slow games down, but should prevent other wound allocation cheese that occurs.
Shots from Overwatch also allocate wounds this way and can prevent a unit from successfully being able to assualt due to taking enough wounds that the first rank doesn't reach the unit.
Regardless of the number of hits actually made, you can only wound and kill models that are in range of your weapons.
No Half Strength blast templates vs vehicles. Templates now do full strength hits regardless where the center hole is.
Independent Characters and Snipers may allocate wounds to visible models in range with rolls of 6s to hit.
Grenades may now be used as a shooting attack.
Unit Leaders (example: Battle Sister Superior) and Independent Characters benefit from "Look Out Sir!" save versus shooting to prevent from taking wounds.
Cover saves are given on a model to model basis, not a unit to unit one. Only 25% of the model needs to be covered though.
Plasma Grenades may be thrown.
Vehicles
Vehicle types now include: Tank, Flyer, Skimmer, Fast, Heavy, Transport, Walker, and Chariot. Vehicles may have more than one type.
Fliers can only be shot on 6s by units that don't have the Sky Fire rule in addition to any rules they get for Hover or Zoom.
Fliers may attempt to
Heavy Vehicles work like the Monolith. They have a slow movement speed but can still function rather powerfully.
All vehicles now have Hull Points.
Disembarking can only be done if the vehicle moved 6" or less and must be placed within base contact with the access point and then moved upwards to 6" from the access point. No more 8"+ bubble from the access points when disembarking.
Count as WS0 when Stationary and WS1 when they've moved in the previous turn.
Unit counts as moving if the vehicle moves, and may only snap fire if the vehicle moves over 6" (up to 12").
Flyers that explode after zooming in the previous turn inflict an S10 wound on all passengers (no armor saves allowed), and a S6 large blast under where it crashes.
Dark Eldar Raiders, Ravagers, Razorwings and Voidwings have 3 Hull Points.
Dark Eldar Venom has 2 Hull Points.
Leman Russ has 3 Hull Points
Ork Battlewagon has 4 Hull Points
Sentinel has 2 Hull Points
Vehicles in Squadrons must stay within 4" of each other
Immobilized models split off from Squadrons and become independent units
Squadrons are hit closest to furthers from the shooter. So the closest vehicle has to be destroyed before the others can be effected
Hull Points/Damaging Vehicles
When a vehicle is glanced 1 Hull Point is removed for each successful glancing hit. When a vehicle suffers a penetrating hit a Hull Point is lost and then a roll on the vehicle damage chart is made (+1 for Open Topped, +1 for AP2 and +2 for AP1, no penalties for AP-): 1-2 Shaken, 3 Stunned, 4-5 Weapon Destroyed, 6 Explodes!). When all Hull Points are gone the vehicle becomes a wreck.
Most vehicles have 3 Hull Points, however some have 4 (examples: Soul Grinder, Land Raider, Ghost Ark, Monolith) and others have 2 (examples: Vyper and Ork Buggies).
Cover
Most things provide a 5+ (to include shooting through units, being inside of craters and being partially concealed) though Ruins give 4+. Vehicles and models now get cover saves if 25% of the model/unit is covered instead of 50%.
Psychic Powers
Units within a certain range have a 6+ to nullify the power, Psychic Hoods improve this to a 4+.
New generic powers are available to most armies with psykers as follows (the list is incomplete at this time but it's been improved upon to give us abetter idea of what we should be looking at for the powers next edition):
Biomancy -
Smite - 12" Range S4, AP2, Assault 4.
Iron Arm - User gains +D3 Strength and Toughness.
Enfeeble - 24" Range, Target unit gets -1 Strength and Toughness, treats all terrain as difficult.
Endurance - 24" Range, target unit gains the Feel no Pain special rule.
Life Leech - 12" Range, S?, AP?, Assault 2, for every unsaved wound the user gains a wound (up to starting wounds).
Warp Speed - User gets +D3 Initiative.
Haemorrhage - Haemorrhage is a focussed witchfire power with a range of 12". The target must pass a Toughness test or suffer a Wound with no armour or cover save allowed. If the target is slain, randomly select another model (friend or foe) within 2" of him. That model must pass a Toughness test or suffer a Wound with no armour or cover saves allowed. If that model dies, continue the process until a model survives or there are no suitable targets within range.
Divination -
Prescience - 12" Range, Target unit rerolls failed to hit rolls.
Foreboding - Psyker (and any unit the Psyker is with) gain Counter Attack and use their full Ballistic Skill when Overwatching.
Forewarning - 12" range, Target unit gains a 4++ invulnerable
? - Target unit rerolls passed armor saves
Perfect Timing - Psyker and Unit ignore cover saves.
Precognition - Psyker rerolls failed To Hit and To Wound rolls and Armor Saves
Scrier's Gaze - Scrier's Gaze is a blessing that targets the Psyker. Whilst the power is in effect, you can roll three dice and chose the result you want when rolling for Reserves, Outflank and mysterious terrain.
Pyromancy -
Flame Breath - S4, AP5, Assault 1, Template
Fiery Form - Psyker gains +2 strength (unconfirmed?), Blaze special (4++ Invunerable?)
Fire Shield - 24" Range, Target Unit gains a 4+ Cover Save
Inferno - 24" Range, S?, AP?, Assault 1, Soul Blaze (?), Blast, Ignores cover
Spontaneous Combustion - Target model takes 1 wound with no armor/cover saves allowed and a small blast template is centeredon them. Any models hit take a S4, AP5 hit.
Sunburst - 6" Range, S?, AP?, Assault 2D6, Blind (?), Ignores Cover
Molten Beam - 12" Range, S8, AP1, Assault 1, Melta
Telekinesis -
Assail - 18" Range, S6, AP?, Assault 1, Strikedown (affected target halves their initative and moves as if in dangerous terrain)
Crush - ?" Range, Roll 2D6, Target takes hits equal to strength (11 or 12 auto wound), AP is equal to seperate dice roll
Gaze of Infinity - Remove models from table, Deep Strike anywhere within 24" of their previous location
Objuration - Target enemy unit must reroll to hit and wounds of 6.
Shockwave - Range 12", S?, AP?, Assault D6, Pinning
Telekine Dome - All friendly units in 12" get 5++ Invunerable
Vortex of Doom - is a witchfire power with the following profile: Range 12" S10 AP1 Heavy 1, Blast* If, when using this power, the Psyker fails his Psyhick test, centre the Vortex of Doom blast marker on the Psyker - in this case, the template does not scatter.
Telepathy
Psychic Shriek - Roll 3D6, unit suffers leadership wounds (?)
Dominte - within 24", must pass a leadership roll or do nothing
Mental Fort(ification) - Unit stops falling back and becomes fearless
Puppet Master - Target model makes an attack as if it were owned by the Psyker
Terrify - Target unit loses Fearless and treats all units as fear causing
Invisibility - Target unit gains shrouding and stealth, hostile units charged by this unit lose counter attack and fight at WS1
Hallucination - is a malediction that targets a single enemy unit within 24". Roll immediately to determine the manner of hallucinations the target is suffering from (roll once for the whole unit).
D6 Result
1-2 Bugs! I Hate Bugs! Something unspeakable has gotten under the victims armour and has begun to crawl around. The unit is automatically Pinned, unless it would normally automatically pass Pinning tests or is locked in close combat, in which case there is no effect.
3-4 Ermmm? All sense of urgency is lost, and the befuddled warrior just stare listlessly into space. The unit cannot shoot, Run, declare charges or strike blows in close combat whilst the power is in effect.
5-6 You! You're a Traitor! Paranoia set in and the panicked warriors lash out at thei comrades. Every model in the unit immediately inflicts a single hit on his own unit, resolved at that model's own Strengths, but using the Strength bonuses, AP values and special rules of their most powerful close combat weapons (if they have any).
Generic Powers are taken based on availability determined by a chart in the Big Rule Book. If taken they are used in lieu of the powers listed in the codex. These powers don't replace powers the model automatically has (like Hammerhand).
Units get a 6+ vs Psychic Powers targeted at them
If the unit contains a psyker of equal or lesser Mastery Level it becomes a 5+
If the unit contains a psyker of higher Mastery Level it becomes a 4+
If you have a guy within 6" of the unit with a psychic hood you can roll as if he were in the unit
If the psyker is inside of a vehicle he can only increase the vehicle's save
Allies
Perks/Penalties based on trust level between two armies. Some armies can't ally with certain other armies and Tyranids aren't allowed Allies.
Can NOT ally with your own army to break the FOC.
Allies require you to take 1 HQ and 1 Troop choice before taking any other options. May take an additional Troop Choice and up to 1 of any non-HQ choice from the Ally's army.
Fortifications
Are bought as part of your army in a 0-1 Slot and count against your army's total points.
Fortifications have Hull Points like vehicles.
Can be upgraded (examples given: weapons with the Skyfire rule and Comm Units (give bonuses to reserves)).
Include the Aegis Defense Line, Bastion, Skyshield Landing Pad and Fortress of Redemption.
Must be deployed inside of your deployment zone.
Warlords
New rule sets that add free bonuses to one of your HQs (the one with the highest LD cost, if tied player chooses) based on a die roll on one of the three tables available (no word if Special Characters can get these rolls or if it's limited to generic HQs only):
Command:
1. friendly units in 12" get to use your LD
2. enemy units in 12" use the lowest LD in their squad.
3. all friendly units in 12" get move through cover.
4. all friendly units in 12" may reroll running.
5. all friendly units in 12" re roll 1s to hit when shooting at an enemy within 3 of an objective.
6. all friendly units in 12" add 1 to charge distance.
Personal:
1. warlord and his unit get counter attack if in own deployment zone.
2. warlord and his unit get furious charge if in enemy deployment zone.
3. warlord and any unit he joins in deployment get outflank.
4. get 1 VP for each character killed by you warlord.
5. your warlord and his unit get FnP if within 3" of an objective.
6. your warlord is a scoring unit.
Strategic:
1. all your units get move though cover for ruins and stealth in ruins.
2. you amy have night fighting on the first turn.
3. your outflanking units get acute senses.
4. while he is alive you may reroll reserve rolls.
5. while he is alive your opponent get -1 on reserve rolls.
6. after both sides have deployed but before scouts you may redeploy 1 unit 3D6", or 3 units D6", may not leave deployment zone.
Terrain
Mysterious Terrain - Similiar to the Magic Terrain rules these are provided as a way to spice up the game when you enter them with effects varying from attacks against all the Psykers on the board to dangerous terrain to the terrain itself assaulting the unit inside.
Mysterious Terrain Table For Objectives:
1 Sabotaged - S4 hits to whole unit,
2 Nothing
3 Skyfire Nexus - Unit gains Skyfire rule
4 Targeting Relay - Reroll1's when shooting
5 Scatterfield - +1 Coversave,
6 Grav Wave Generator - Unit charging halves charge range
Missions
3 Deployment Types - Pitched Battle, Short Table Edges (12" in) and a triangle shaped deployment that cuts the table into fourths, corner to corner style.
6 Scenarios with various objectives and situations.
Secondary Objectives (add 1 VP) - Slay the Warlord (kill the enemy HQ (perhaps Warlord?)), First Blood (destroy an enemy unit, no word if vehicles will count), Linebreaker (having models in the enemy's deployment zone).
Monstrous Creatures
All attacks are AP2 unless using a weapon that makes them AP1..
Gain Smash versus vehicles, lose 2D6 penetration rolls.
Winged MCs can use Vector Strike against Vehicles. Inflicts D3+1 Hits at Unmodified Strength (sorry, no Smash) at AP2.
Winged MCs may make a Swoop Movement (similiar to a Flyer's Zoom)
While Swooping the MC may fire two weapons.
Vector Strike counts as shooting one weapon. The MC may fire a second weapon at a different target after Vector Striking.
Winged MCs don't count as Flyers and instead have their own specific rules.
via MadCowCrazy
Flyers
Aerial Support
Flyers must being the game in Reserves - it takes time for a Warlord to organise and coordinate air support.
Flyers and Measuring
Flyers have flying bases that suspend them above the battlefield. However, distances are still measured to and from the Flyer's hull, with the exception of the vehicle's weapons and Fire Points, which all work as normal. The base of the Flyer is effectively ignored, except for when:
-The Flyer is being assaulted, in which case the models may move into contact with the vehicle's hull, its base or both.
-Models are embarking or disembarking from the Flyer, in which case the base of the Flyer is used as the Access Point.
Flyers and other Models
Models that physically fit under a Flyer model can move beneath it. Likewise, a Flyer can end its move over such models. However, when moving this way, enemy models must still remain 1" away from the base of the Flyer, and the Flyer cannot end its move with its base within 1" of other enemy models.
Zoom
Flyers can usually only make a special kind of move called Zoom. Some can also Hover - see page 81. Zooming allows the Flyer to move at fantastic speeds making it very difficult to shoot down, but limiting its manoeuvrability. If a Flyer Zooms, it has a Combat Speed of 18" and Cruising Speed of 36". However, as a certain amount of forward thrust is required for the vehicle to stay in the air, a Zooming Flyer can never voluntarily move less than 18". If a Zooming Flyer is forced to move less than 18" in its own Movement phase, it is automatically Wrecked.
To represent its limited manoeuvrability, a Zooming Flyer can only make a single pivot on the spot of up to 90 degrees before it moves. Thereafter, it must move directly forwards in a straight line. In a turn in which a Flyer enter the board from reserve, it can do so facing any direction you wish, providing that the resulting move will not carry it off the board again. A Zooming Flyer can move over intervening units and impassible terrain exactly as a Skimmer. In addition, a Zooming Flyer does not have to take Dangerous Terrain tests even if it starts or stops over difficult, dangerous or impassible terrain. Finally, models cannot embark upon, or disembark from, a Zooming Flyer.
Zoom, Tank Shock and Ramming
Zooming Flyers cannot Tank Shock or Ram nor can they be Tank Shocked or Rammed.
Zooming and Shooting
Flyers have sophisticated targeting systems designed to work at the fastest speeds. Zooming Flyers can fire up to four of their weapons using their full Ballistic Skill if they have moved at either Combat Speed or Cruising Speed that turn.
Assaulting Zooming Flyers
Due to their high speed (and presumably high altitude)...
Zooming Flyers cannot be assaulted.
Leaving Combat Airspace
It's quite likely that a Flyer making a Zoom move will.... the board, either deliberately or by accident. If this happens the Flyer is said to have left combat airspace - it then enters Ongoing Reserves (see page 125). A Flyer that leaves combat airspace must Zoom back on when it returns from Ongoing Reserves, even if it has the Hover type. Flyers and Damage Results Zooming Flyers follow the exceptions given below.
Locked Velocity
If a Zooming Flyer suffers an Immobilised result, its velocity is locked. A Flyer with Locked Velocity cannot change speed for the rest of the game, but must continue to Zoom at Combat Speed or Cruising Speed (whichever it was using when it suffered the Immobilised result). Once a Flyer's velocity is locked, it cannot Evade and cannot move Flat Out, however with Locked Velocity you can still turn before it moves as normal and if it leaves the board will enter Ongoing Reserves.
Crash and Burn
If a Zooming Flyer is Wrecked or Explodes, its flaming hull rains down on the battlefield. Centre a large blast marker over the Flyer - it then scatters 2D6". Any models under the blast marker's final position suffers a Strength 6, AP- hit. The Flyer is the taken off the board. If the Flyer is also a transport any models within suffer a Strength 10 hit with no armour saves allowed. Survivors are placed anywhere within 3" of the marker's final position and in unit coherency. Any models that cannot be placed are removed as casualites.