Fallout 3
I'm on my third playthrough now, I'm being an evil character to have different experiences. Honestly, it doesn't suit me, I keep feeling compelled to be good and have to stop myself. D:
Left 4 Dead
I bought this about a month ago (I know, I'm really late to the party), but I've been fortunate enough to find some good games going on still and made a few new friends to play it with, too! I've played all of the official campaigns through at least a few times now. I'm loving this game.
Minecraft
This is my relaxation game. I alternate between exploring and building in single player and joining some friends on their server and helping out with their epic city project.
Cryostasis: Sleep of Reason
I bought this during the Christmas sales last year and only got around to trying it now. I'm liking it so far. It's a mysterious, immersive game. I had a lot of difficulty getting it to run well though. My PC is well beyond the recommended specs, but I still had to put all the settings down to low (and run it at the pitifully low resolution of 1024x768) to get it to run smoothly at all times.
Operation Flashpoint: Cold War Crisis
I've played this semi regularly for years, either to do single player missions, mess around in the editor, or play LAN games with family. My favourite "military" game of any sort by far.