I would have to say Skyrim.
But the list of games I've played are quite short:
Assassin's Creed 1 (Boring)
Sleeping Dogs (Sorta fun, kinda like GTA)
Dead Rising 2 (Looked fun, was meh)
Syndicate (good game)
Dead Island series (I liked it a lot)
Tom Clancy's Ghost Recon (fun game)
Uncharted series (Super interesting and fun to play)
Tomb Raider (2nd favorite game)
Dishonored (too short)
UFC Undisputed 3 (was fun for 1 day)
Nascar (meh)
Resident Evil 6 (I liked it I don't care if it wasn't really RE, I liked the action and zombies/BOWs/infected)
Resident Evil Revelations (change underwear)
Infamous series (YESSSSSSSSSSSSSSSSSSSSSSSSSSS)
The Last of Us (Amazing game)
Watch Dogs (I liked the concept )
Thief (better version of Dishonored imo)
Outlast (good horror game)
Dead Space (scary at first)
The Darkness series (favorite game at the time it came out)
Multiplayer:
League of Legends (I just play it cause everyone else plays it)
Crossfire (meh no)
COD series from Black Ops to present (I like the campaigns, even though most people get it for multiplayer)
Runescape ()
BattleOn/Dragon Fable ()
Guess I just really like the 1st/3rd person adventure games that just look amazing and are sorta open world. (and as you can see, I really only like single player games except League)
So, favorite game? On top of that feel free to post a laundry list of games that you've played and what you think of them, mine is kinda short but yeah.