Just because someone lists games that came out this year, doesn't mean they haven't read to OP... except for Vanin of course. Yes, all 5 of my games were from this year, but that is because this year has been a great year for games and I loved every game I've listed.
Portal 2-Great game, makes you think, co-op with a good buddy was hands down the most fun I've had playing a game in a long long time. I mean this is the kind of game that people that don't even really like games would like.
Skyrim-Never played any of the Elder Scrolls games before but I heard too many good things about it to pass up...only been playing for a couple days but it's a good pick for sure
Battlefield 3 (better, more tactical multiplayer than MW3 IMHO if that is what you are looking for). It plays really well on PC minus all the bugs with origin and server finder because origin sucks, hopefully that will improve. Co-OP blows junks all things considered, so don't be looking to get more than an hour or two out of that
MW3-More diverse/interesting single player IMO than BF3 (though both are good), Co-Op is better and longer as well. But if you haven't played any CoD games yet, go for Modern Warfare 1 aka CoD4
Terraria-Cheap and simple entertainment
Magicka-Funny as hell, kind of goofy but it's also cheap so I'd say it's worth the money, has some expansion packs now but haven't gotten to those myself
Dead Island-Good game, haven't quite finished it yet myself (too many damn games to play at the moment). Something about all the zombie guts makes me really happy inside.