You have to experience Limbo for yourself.
Very cool game. Really neat puzzles and awesome visual style. It's definately worth buying. If I were to say that games are art Limbo would be my first example. It's really something else.
The excellent use of foreground and background really gives you a sense of being lost in an otherworldly realm. The lack of music and use of creepy sound effects is great. Every second of the game, from start to finish has a perfect atmosphere. The ending is great too.
The majority of the puzzles will kill you the first time around, in really brutal unsettling ways. But you'll start off right where you left off anyways so it's not a big deal. The game has no levels and never really loads. It fades out when you die and back in when you respawn. Other then that the game just keeps moving, there are no "you've reached a new level screens" or anything like that. This makes Limbo feel really organic. The controls help give it this organic feel too, the have a really nice weight to them that you just have to experience for yourself.
It's around 3-4 hours long but it's a really great 3-4 hours. You'll probably want to play it again to find the acheivments. It's got good acheivments and avatar awards too. I strongly reccomend this game, it's one of the best to come out this year.