What a fantastic game. While there's not as much narrative as Portal (you only get the signs that pseudo explain the puzzle after you solve it), this game is right up there in terms of puzzles. The game does an amazing job of teaching you what sorts of things you can do without blatantly telling you. And many puzzles/rooms have multiple different ways of being solved depending on which strategies you try. And man, the mindf*** this game can put on you at times.

Gave me 10 hours of challenges, with a bit of frustration at one point until I realized I missed an obvious puzzle solution, and great pride in solving puzzles. If you like Portal or Q.U.B.E. this should be right up your alley.