This should be easy, since I only own 11 360 games, ( Excluding XBLA games) and I don't even have to think, to know which one doesn't make the cut. (SoulCalibur IV.)
10. Bayonetta
9. Dead Rising
8. Just Cause 2
7. Assassin's Creed II
6. Mass Effect
5. Fallout 3
4. Grand Theft Auto IV
3. Red Dead Redemption
2. Mass Effect 2
1. Bioshock
EDIT: The original Assassin's Creed, Arkham Asylum & Bioshock 2 would've probably been on the list, if I hadn't played only the PS3 versions of those games.