To begin, he is not an archon, he cannot take a Court of the Archon. However he comes with amazing wargear for his cheap points with good stat lines. WS6 BS6 S3 T3 W2 I6 A3/4 Ld9 Sv4+. He comes with a Blast Pistol, Shadow Field, Plasma Grenades, Ghostplate Armour, Combat Drugs, and The Serpent's Bite (two 2+ poisoned close combat weapons that on a 5+ don't allow armor saves.) That is a ton of wargear.
He has the obvious Fleet, Night Vision, Power from Pain, and Independentt Character special rules. The fun stuff is the following;
The Serpent's Venom; Pick a unit of kabalite warriors of trueborn and start with them at the beginning of the game (yes you must, as the rules currently sit). All splinter weapons in that unit are upgraded to poisoned 3+. This could be extremely nice if you grab a bunch of shard carbines and splinter cannons for your trueborn.
Contraband: Roll two dice when determining which combat drugs are available and choose which one you want. (no you cannot re-roll doubles) This will really help armies that want to run a wych theme, or that want to just run combat drugs in several units.
Low Orbit Raid: Deepstriking Raiders, Venoms, and Ravagers. They can all do this without any upgrades. To top it off, they can now deploy as well, since this special ability does not count as retrofire jets which do not allow disembarking the round you deepstrike. (no you cannot assault after deepstriking).
What the Duke brings to the table is enhancing all combat drugs, aiding a warrior or trueborn unit, and finally allowing all Raiders, Venoms, and Ravagers to deepstrike without paying for retrofire jets.That's alot. When playing with the Duke, your army should very much use the units he effects. If you are not using Duke Scliscus and you are playing with at least 2 of the 3 unit types he effects, you should do a serious sit down and contemplate whether or not the Duke's bonus's would help your army.
While I find that my HQ choices are as tight as my elite selections, I have already tested the Duke. What it comes down to for me, is weighing the effects of my other HQ selections vs his. He puts in a tough fight for my top picks. As an HQ he is excellent, and there are not too many other HQ's in 40k that give quite so much synergy (as everyone likes to call it) to so much of your army.
Not really knowing where the dark eldar are coming from can be hard to deal with, and dark eldar do extremely well the first round or two they appear. Setting up to use the webways for fast moving units for assaulting and deepstriking all your skimmers for firepower, the round they appear, sounds fun. With the webways, you would be able to reach anywhere on the table with your wych assault units, and strike from anywhere with your deepstriking firepower.
You would use a full unit of trueborn with a haemonculi and webway for position, maybe two since the Duke needs one. Lots of wyches and some reavers that could emerge from the webways with lots of deepstriking raiders/venoms for every unit you can muster. Your ravagers would come in guns a blazing, deepstriking in for firing advantages. The only real issue for me, is that's not normally my style of play. Even if the deepstriking ability is just used as a back up vs alpha strike lists.