stuffty PC ports.
(i.e. Saints Row 2 :c)
non-coop games. I really enjoy games like L4D or alien swarm because you don't have a choice but to rely on your friends. (Well, that's the way it usually is anyway)
Whereas in TF2, you can run off being independent and you can still get stuff done. Not only that but you're playing against other players which can form rivalries, and I'm not particularly fond of rivalries :c THAT AND EVERYONE BUT ME SEEMS TO BE SUPER PRO AT forgetIN' TF2 DAMNIT