Going on just my three favorite games at the moment, that'd be Dark Souls, Skyrim and XCOM. Two out of three of those aren't exactly noobie friendly, so I'd probably recommend something along these lines.
1)Skyrim, since it's pretty, not exactly difficult, and rewards faffing about. One of the noob-friendliest RPGs since Pokemon.
2)Starcraft 2, while the online community is one of the most intimidating out there, the campaign is actually really good and the game as a whole does a great job of teaching someone who's never seen a mouse before how to play an RTS. Not to mention his twitch reflexes from CoD would actually translate very well into micro-managing in this.
3)Something Mario, preferably one of the newer ones, since recommending old school games to people who haven't really tried anything outside of their comfort zone can really backfire. Mario may be the exception, but even then I'd try him out on the Mario Galaxy games.
Alternatively, I'd just invite him over, let him dick around with your collection so he can see what genres he likes, and then make recommendations from there.
EDIT- Oh hell, how did I forget about Portal? I'd prioritize that over Mario, but really, just make him play a bunch of different games, and see what interests him the most.