This was tough.

Batman Arkham City
Zelda Skyward Sword
Dark Souls
Portal 2

All are great games (and yes despite SS' annoying wireless controls)

Torn between Dark Souls and Batman but I went with Batman.

Skyward, imo, has the best dungeons in the series.

Its either Skyrim or Dark Souls.

OTHER-
Two games spring to mind for me that released on PC that were huge for me. One was very impactful and spawned several sequels.
The other was amazing fun, but the studio was wedged by the big Sega/Gearbox drama of the time, as well as Games For Windows Live.  They closed fairly shortly after release.

The impactful game was To The Moon. A very smartly written RPG Maker game about two doctors travelling through an elderly dying man’s memories to solve the mystery of what will let him die happy.

The amazing fun game was Section 8: Prejudice. An amazing multiplayer shooter with a great variety of fun.
Sadly no longer purchasable or playable without GFWL workarounds, but it really was an amazing fun time that nothing else has dared to replicate.

My game of 2011 is Section 8: Prejudice.

After reading some more of the love towards Portal 2, and diving further into my memories of both Dark Souls and Portal 2, I'm starting to rethink my positioning of those two games in my top 50. Which one has aged better, Portal 2. Which one would I replay, Portal 2 for sure, Dark Souls likely not. The boss battles have only grown in negativity in my memories. Many I never completed myself, just waited for high level co-op summons to help out. Another strike against replay-ability. The map design is still brilliant, yet the game play is getting less and less appealing as I grow older.

If there happens to be a run-off, I'll likely change my vote to Portal 2. Gonna update my top 50 now, both will remain top 30 for sure, yet Portal 2 is moving up, Dark Souls moving down.

For sure, FromSoftware greatest strength is definitely map design and creating compelling worlds, they're masters of the 3D Metroidvania. Their game design I'm less impressed with though, always ends up a bit of a mixed bag in my eyes.

Hard choice Minecraft was a phenomenon on YouTube bringing creative mechanics to content creators, however I don't consider it a notable game of 2011 as it was already played a lot before in beta.

Portal 2 is perhaps the best all-time puzzle game, everything is perfect, level design, gameplay, voice acting, but I think it was less impactful than the other 2 that remain to be mentioned.

Skyrim improved everything in relation to Oblivion, raising the bar for Western RPGs and OW games
but for me the winner should be dark souls, it revived the sense of difficulty and reward of games from the 90s, exceptional level design of connected areas, memorable battles, brilliant use of online, as well as things that transcend the game itself, it created a subgenre, since then its formula has been widely copied, in addition to having influenced dozens of games, cultural impact on the industry, it has become synonymous with difficult games , at some point everyone must have seen something like mario something is the dark souls of the mario series. After thinking about it, it's actually an easy choice.

Honourable mention goes to Pushmo/Pullblox. That downloadable puzzle game on 3DS was really good fun.

Skyward Sword only because I never played the others on the poll.

Another year I expect to be alone, but I'm going for Catherine. Excellent and truly unique game