This is just my top 20 based upon my enjoyment/experience with them, this isn't set in stone or anything or what I think are the actual best games of 2011. Obviously this is based upon bias and it isn't going to follow any strict score system.
Portal 2: Portal 1, was an unexpected enjoyment for me. Not anticipating very much I popped it in after staring at tf2 for a while. What began as indifference ended in lots of fun and I ended up finishing it all in 1 sitting in at around 2 am. Portal 2 brought out new story and gameplay elements not found in the first. The difficulty was increased and I got stuck four or five times, but part of the fun about Portal 2 and puzzle games in general is outwitting the puzzle and figuring it out by yourself. The co-op experience was astounding and there still remains a lot of user generated content that impresses me to this day.
Catherine: I learned about Catherine through its wacky pre-order bonus including the main character's boxers and other goodies. After watching a few trailers I was hooked on any new content that came out about it. I do not get hyped about games because of many disappointments in the past but it was hard for me to not get excited for Catherine, and Catherine didn't let me down. Combining incredibly challenging puzzle segments and compelling story this game easily makes it to my top 3.
The Elder Scrolls:Skyrim
Minecraft 1.0 release: Yes I know Minecraft didn't get created this year, but it was formally "released" which I think should count. 1.0 brought with it a lot of new content including creative mode which has really gotten me back into the game. Hopefully this release doesn't mean a lack of additional free content to be released by Mohjang in the coming year.
Payday The Heist: I usually don't pay full price for games but I took the plunge with Payday and I was pleasantly surprised. Although bare bones at first, with the lack of many key features, it was still a great co-op experience one I haven't experienced since my first time playing L4D. Four player bank robbing is just epic, and with new heists coming out eventually there's plenty of re playability.
Red Orchestra 2: Heroes of Stalingrad: The first Red Orchestra was a hyper realistic fps which frankly was balls to the walls hard. The Red Orchestra series loses a little realism (you don't die in 1 shot to the leg anymore) in its newest addition, but it adds a lot of mechanic improvements that make it more fun for me than the original. The realism that's still there meshes well with the improved movement and new squad based/commander revolving combat.
Total War: Shogun 2: Ever since I was a kid I've loved medieval combat and the feudal wars of Japan are no exception. Once I heard that they were releasing a new Sengoku themed total war game I couldn't help but go "Aww yeaah." Much of the HUD clutter found in total war games has been cleaned up and pathing issues that plague the series are drastically improved from previous games as well a much more balanced unit roster.
SSFIV: Arcade Edition: Adding four new characters and rebalancing the old ones doesn't sound like much, but for a newcomer to the Street Fighter scene this equals a lot of content. Although many might not be happy with the relatively small changes between titles, speaking as someone who waits for a few editions to buy you really get a good product. I don't agree with Capcom's business model of adding 1 or 2 new things and reselling for full price but I won't let that impact my enjoyment of a good game.
Rock of Ages: Another game by Atlus, but this one totally different. This game plays out like a Tower Defense style game with you taking turns rolling your giant bolder to reach the enemies gate and building up your defenses while your boulder is out of commission. With 2 player online and local it really is a blast to play.
Melty Blood Actress Again CC: I'm a big fan of Tsukihime so when I heard there was a fighting game series of it I was exstatic. Fast forward a couple years later and tight controls and a big roster have helped keep my love alive. Current Codes adds 2 new characters and made the game available on PC, finally adding online play to the most recent edition.
Worms Ultimate Mayhem
The Binding of Isaac
No More Heroes: Heroes Paradise
Arcana Hearts 3
Mount and Blade: With Fire and Sword