Skyrim is going to get tons of accolades all over this year, and deservedly so, but Deus Ex: Human Revolution pulled me into its world more effectively than any other game in 2011.
It didn't do everything right. Obviously, there were the boss battles. They required a narrow combat approach, playing to some of Deus Ex: Human Revolution's weakest elements. But those encounters were only disappointing insofar as they contradicted the fluidity of gameplay styles and approaches the rest of Human Revolution offered.