Left 4 Dead
I've found myself really excited for Left 4 Dead. Valve is responsible for many hours of FPS fun, with Team Fortress 2. Since the demo has come out now, I've gotten to give the sample levels a run through and it works pretty well. The co-op play really seems to work, and the game really rewards you for sticking together. Looks like I'm going to have to drop some cash for this one.