Team Fortress 2, I avoid it as much as possible because it's so addictive to me, I love the art style and the feel of the game. I've got like ...800+ hours in the game though so avoiding isn't easy.....and I got the figures ....and a actual TF2 soldier grenader cap ........D: Say what you want about FPS being dumb or same-y every match played always goes different and is always exciting.
Sonic's Genesis/Mega Drive games, need I say more? Fun platform-y titles that you can do a level or two in and be satisfied between things through the day.
Final Fantasy Tactics, much like Team Fortress 2, the art, the style, the way you can experiment with all sorts of classes and load outs, and the music by Gordon Freeman do I love the music.
Saints Row 3, I've always been partial to the GTA games till 4 hit me in the face with social simulation nonsense. These titles kept me sane to be perfectly honest, in school I'd come home play for a bit and run over a bunch of people and just vent. Today I have a lot of issues at home some of you may know, so Saints Row is the new replacement for GTA basically, helped by co-op, MAN that is fun. Way, too much fun.
Dunno if Mass Effect series counts yet, I've played 1 a bunch for various reasons but I'm going through the series again, and finally, FINALLY got to play some Mass Effect 3 multiplayer with friends, it took 2 freaking years but I got some friends playing with me. Happy? You bet.
There's some I'm likely missing but I dunno, there's a lot to be said for anyone I think with games like these, complicated or simple there's always one game someone wants to play again.