Battlefield 3 looks amazing on max settings with the new frostbite 2 engine. Many mods out there do lots of things, like HD texture packs and depth of field mods. Even minecraft looks great with a nice HD texture pack and glsl shaders.
For my money, I have to say Trine 2. It's hard not to choose Rayman Origins, since I don't think I've seen another game capture that sunday morning cartoon appeal nearly as well, but Trine 2 is just gorgeous.