Love Space Marine, shame it didn't sell better.
My only criticism is that Orks significantly outstay their welcome, and their replacement isn't all that fun to fight against, especially on higher difficulties.
While I'm not into competitive MP, I had some fun with it, though I consider locking perk slots behind levels to be obnoxious bullshit. You are seriously crippled for the first several levels and just hope your teammates don't mind you being dead weight.
Horde mode is also nice. Only once managed to get to the final wave, then I spent 20 minutes trying to find ammo because those fuckers eat bolter shells like I candy.