[PPharoah]

Call of Duty 4 has a single player campaign with intel pieces that must be picked up to unlock new modes, and then achievements that must be unlocked not only on the regular difficulty setting but Veteran as well. When he is done with that he can move to the Multiplayer Online, 55 levels, he can create his own class, and then start over at level 1 for prestige, gaining new unlocks all the way! GREAT bang for your buck here.

Mass Effect-although all singleplayer this game is so deep it doesn't need multiplayer, 50 levels his first time through, then 10 more levels on the second runthrough, the ability to select your existing character for the second runthrough, a HUGE galaxy map with many systems to explore, upgrading of weapons and armor and the ability to play as a Paragon, Renegade, or combination of both further add to the replayability in this game.

Assassin's Creed is not even a consideration here, it's a rental game ONLY, once you have played for an hour or two you have seen everything there is to be seen. He will go through it way too fast.