I'm not much game oriented: I prefer real boardgames instead of computer games.
However, Limbo is a real gem.
The graphism is a pure amazement of simplicity. The music is an essential component of the tension. It's really terror building.
Not very difficult, so very fun to play.
Wait for the middle of the night, stay alone, put your sound on and launch Limbo... You won't regret it. Or maybe you will, but you'll love that.