Akimbo

The multi-player alone is worth the price -- simply the most mind-bending fun I've had playing couch co-op. The single player campaign is a bonus. The writing is superb, the puzzles are fantastic, and the additions they've brought to the Portal "universe" just improve the game.

One of the most beautiful, creative, puzzling, and enjoyable games I've played in a long time. Fantastic art, great dialog, clever puzzles, with lots of extras to keep things interesting. It even features a good built-in hint system with progressively more revealing hints in case you're really stuck.