Inside the New Space Marine Codex: from Warhammer TV
You can see it here....
Primaris Marines have 3 Primaris Organs.
Primaris Marines Coils of metal around their sinews that enable to them to be much stronger and more durable. A Magnificant Amplifier that amplifies the usage of their organs, and a Furnace organ that floods their bodies upon death with adrenaline hormones to give them a huge burst of energy just before death. This shows up with more wounds, more attacks etc.
The Space Marine Codex has rules and chapter tactics for 8 Marine Armies with relics, Warlord Traits, etc.
Again its been said again that Primaris Marines are not replacing anything, but are integrated into the Marine Companies.