There's a few I haven't played yet like Zelda and Portal 2. Right now I am inclined to say it's Arkham City simply because when you compare it to games like Skyrim and Battlefield 3, it is a programming marvel. So far it has been bug free and has a level of polish on it that Bethesda only dreams about. If Skyrim or BF 3 were programmed as well as Arkham City, either one would be my favorite hands down.
Even if the open windows of science at first make us shiver after the cozy indoor warmth of traditional humanizing myths, in the end the fresh air brings vigor, and the great spaces have a splendor of their own - Bertrand Russell