Limbo is a game that has been released on Xbox Live Arcade some time ago, but I've only now found time to play it.
It is a very nice game - albeit a bit on the short side: it took me about 5 hours to finish it. But this is the only negative bit I can think of. Everything else about the game is very nice. It is very polished and it's a charm to play. You have to think about the puzzles for some time but the learning curve is okay and there were no unfair bits.
The game is black-and-white only (with shades of gray) and you play a boy that apparently got lost in a forest (this is how it starts) and you want to get out.<
The game mechanics are very simple: you can only move around, jump and hold on to things to drag them around (or press buttons, etc). In this regard the game is very similar to Another World (another very good game worth playing).
The puzzles are all phyiscs-based and because of this the aforementioned fairness is achieved: sometimes you just have to think a bit longer how to solve a puzzle but it is always logical.
The game is somewhat violent because it works using the "learning by dying" principle and if you don't enable the gore filter, you'll see the poor boy being halved, stabbed, squashed,... many times. However, since he is only a black shape, it's okay and won't put you off playing. The game uses many (and only) auto-saves to track your progress and you never feel punished for dying because you'll get another try straightaway without having to replay more than a few seconds.
"Learning by dying" works really well (and is also used in Another World): You don't have to worry about a "health bar" or rewind time or...
The difficulty of the game is just right and it gets harder as you progress through the world: you get to use more objects to solve the puzzles or will have to think of new ways to use physics to achieve your goals. However, one annoying bit is that also autosave points get moved further apart even when there is no need for it. This only happens in the last few "chapters" of the game though.
All in all it is very much a game worth playing and a very polished experience - kudos to the developers!