Best Xboxlive FPS:
Halo2 [No doubt, those who oppose suck]
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Call of Duty [also good online]
Battle Field online [One of my favs, but not really good if you compare it with the PC version]
Best Co-Op game:
Ghost Recon adwanced Warfighter [if you manage to connect to a game it rocks]
Splinter cell Chaos theory. [One of the best and well done co-op games evver]
Kameo / PD [i didn't like them]
Racing:
Burnout Revenge 360 [Can't get more action in a racing game and it has good Live modes]