Tim Schafer's Double Fine is basically one of the most creative game development organisations in the world right now. Fact. Here's a trailer for DF's latest XBL outing, Trenched.
Basically, it's more of a 'satire' on war-gaming than Bulletstorm could hope to be. The Army, Navy and Airforce are all dead, so it's left to the Mobile Trench Brigade to work with its allies all over the world to fight the alien scum.