Antichamber is pretty awesome, and I'm loving its puzzles. It's a fantastic combination of trial & error and learning how the game thinks. I've seen people try to describe its puzzles as non-Euclidean and non-linear, but I don't really know what the exact phrase would be. Either way, any game where the "physical" world is so completely undefined is fine by me.
-edit- Retrovirus is a really nice Descent throwback, too. I wouldn't call it a big PC day, but I would call it an excellent one.
James

