I just got my Xbox last week and have only played NFL2K3, Project Gotham Racing and Sega GT 2002.

PGR is a pretty fun game. I'd recommend buying it.

NFL2K3 is pretty tough. This is my first console since PS1 and I haven't really played any football games since Madden 99. The AI is great and it's not easy at first, but it's real fun to play. I'd definitly recommend buying this game, especially since it's an Xbox live game.