Got the demo yesterday, and I have to say I'm completely loving it, and can't wait for the full game (preordered the Collector's Edition for the Xbox 360). The combat is as bloody and visceral as could be hoped

My only complaint gameplay wise is the lack of a parry/block action, though I don't know how hard that would be to smoothly animate switch between those kind of moves and the killy moves.
@captaincolhoun: You might be interested in picking up the Elite Armour Pack then, it's got a better detailed version of Space Wolves to use in the multiplayer (includes things like wolf pelts etc. rather than being a pallette swap, which is presumably what you get in the standard box).
I can perhaps see this game being expanded with DLC campaigns to represent other chapters and against different opponents. They might experiment with different races being the PC in DLC or perhaps in new games, but I think it was smart to go with SMs first; they're the flagship faction for 40K, so if you're gonna have one to try, Astartes makes the most sense. Also, they're the most 'all rounder' individuals in the game, so again, better to start with them, before going to races that slant towards very specific styles (i.e. hyper specialisation with Eldar, range focused Tau etc.)