I just downloaded the Kill Team ebook, and it looks like a hell of a lot of fun.
Here's a quick breakdown:
200 points max
0-2 Troops, 0-1 Elites, 0-1 Fast Attack
No models with 2+ armor saves
No vehicles with a combined armor value of more than 30
Each model acts independently
One model is designated as leader, rolls for a Warlord trait unique to KT
Three models are marked as Specialists, and choose a special skill
Opponents can be routed and sent running if they lose half their forces
Small attack forces, games don't go too long, and the missions in the book look pretty good; it's also pretty easy to develop your own missions
I'm going to build myself a Chaos Kill Team. I just haven't decided what direction to go. Thousand Suns are pricey, but they can wipe out any infantry under these rules. Plague Marines are tough as hell. Noise Marines have a good chance of downing whatever targets they choose. Berserkers can hit hard in close combat. I'm ruling out Khorne, since this game seems to be more shooting based. Either way, Cultists can fill out any remaining points.
Of course, a full Raptor pack might be fast and fun...