Don't forget HALO too. You need to play HALO first before getting into HALO 2.
I don't know of any other good games for the XBox since I don't own one but I did watch some TV reviews about some of the XBox titles. Anyway, some of them that I do know of are Call of Duty 2: The Big Red One (I hope I got the title correct), Tom Clancy's Splinter Cell, Freedom Fighters and Mercenaries to name a few.