Whats a good game to give my friend as a gift?

He already has Call of Duty modern warfare 2 and assassins creed 2, so what game should i get him?
I was thinking maybe left 4 dead 2 but he never bought the first one, not sure if he just didnt have the cash or if he didnt want it.
and hes 19, so dont worry about a game being too mature or anything, lol:p