Wonderful single-player mode as expected, and a surprisingly strong co-op mode as well. Great expansion of the universe from the original game. Strong design throughout. This game is frankly just about as close to flawless as any game can be.

Expansive levels that make Portal look like a tech demo, with quite a few new fun mechanics and a lot of back-story about the Aperture Corporation. It's about three times as long as the original, and once again ends with fantastic music.