magicka is a good game to play by yourself and if he wanted to play multiplayer. Its hilarious and has lots to explore, there are also many many references to pop culture I'm sure he'd love
Torchlight 2 is a great game, a kind of diablo 3, you probably know it. You can play it on singleplayer mode, or multiplayer, with your roommates, what would make even more interesting! Magicka is very funny too.
Day's Day Off - Magicka
one of my favorite games to play and he cna also play it with anyone of hi sfreinds/fans that have it its like 5 bucks on steam right now and has huge story depth and is a lot of fun ...
diablo:hellfire (diablo will always be great, player mod made it better. requires a bit of setup to run correct though) Metroid prime series (I think Sean would enjoy it, great music and environments)
Super Story Games
I'll just list off some of my favorite games --good game play and good stories-- in order from best to not-best-but-still-awesome:1. Dishonored. This is practically a classic already, what more can I say?2. Spec Ops: The Line. This is some ...