The listing, Portal 2 (PC+Mac) [Steam] has ended.
Up for grabs is the sublime Portal 2 on Steam. The first portal was unique, fun and memorable... but Portal 2 blows it out of the water. It looks better, introduces new mechanics, tightens and makes smarter, the puzzles and really comes into it's own with some spectacular writing. It's a game I've personally enjoyed the hell out of and now want to share that with you :)