At this time the Call Of Duty game is the best game there is now. But before you buy make sure that he does not already have the game. He may not like this type of game so this may not be the best for him. You know his likes so suprize him.
Adding to that bit of info above mine, my brother loves all these games.
Mass affect 1 & 2 (specially the second) gears of war, call of duty black ops, modern war fare (any version if he doesn't have one of them) lost planet, starwars 2 battlefront, crackdown, and prince of Persia.
Call of duty black ops. But i would see what games he already has, and note about what kind hes interested in. There are many genres of games just like music, but if he does not have the Kinect for Xbox then i wouldnt get any games that require that. Also online games, if he does not have internet for his Xbox then that also limits the posiblities of different games. I hope this helped.