#2 Portal 2
Portal 2 is the FPS physics game that brings a beautiful finale to the Valve series, which began with a shorter game from the mind of Kim Swift and followed up with a comic book to tide people over.
Portal 2 offers all-new puzzles, a slew of intriguing new gameplay mechanics (many of them goo-based) and a co-op mode in which you and a friend solve test chambers as bots Atlas and P-Body. And, oh yeah, singing turrets.
