Elder scrolls: Morrowind, Oblivion, Skyrim. I used to play Arena too, much love for the Elder Scrolls games (except ESO which I ignore the existence of as the game is too focused on selling to "mainstream ideals" to be as good as the other elder scrolls games.)
Defiance (pre- free to play) One of the first 1mil damage counts against the big monkey boss when it first came out! A great fun game if you're into shooters in apocalypse settings, also fun if you like driving around and being a hired gun, though for a multiplayer it lacks in decent team play community.
Lord of the rings online: Lots of time and money invested in this game long ago, maybe I'll go back to it one day, but not too soon.
Lego Universe: Why oh why Lego did you give up on this fun little gem!
A plot of land to build your own creations on! Fun easy to play adventures to collect more blocks to build with, or money to buy the blocks!
A shame they wrote it off.
Space Engineers: Because space and building is fun!
Had the pleasure of meeting their lead Dev Marek Rosa by pure chance during a traditional Czech/Slovak meet on High Tatra!
Landmark: I really should play this more with my gaming partner! We intend to build either a goldfish or pyramidion once we get settled into the game.
Kerbal Space Program: Because launching your own Kerbal Minions into orbit around the planet is fun, and setting challenges for Jacob is fun too!
Mass Effect 3 (PS3) Because reasons!
Rage (PS3) Because apocalypse reasons!
SSX Tricky and SSX (PS3) because snowboarding is fun.
Age of empires, 1, 2 (pc) RTS at its retro-best.
Toy Commander (Dreamcast) because it reminds me of when I played with toys as a kid!
Life Is Fiedal (your own) though its been a long time since I played, I look forward to the MMO's release.