Limbo

Limbo is a game that knows what its trying to do and does it very well.  Unfortunately, it's not trying to do that much, and so the end result is a bit emptier and a much shorter than you would hope.  It might be worth it to you as an experience, but if your gaming budget is tight, I can't really recommend you buy this over many other XBLA titles with more depth. 
 
Limbo is in essence a puzzle platformer.  You'll need some logical thinking, pinpoint timing, and quick reflexes in order to get through the various chapters.  There are a great variety of puzzles with many different mechanics - buoyancy, gravity, magnetism - and more than once I had a joyous "aha!" moment as I finally noodled through a puzzle.  You'll end up using some trial and error at times to get through, and some parts require near platforming perfection, but nothing is really all that difficult compared to harder puzzle games or harder platformers out there. 
 
The story and style are both as minimalist as can be.  Beyond a line of text in the XBLA game description, there is no text in the game, there is absolutely no dialogue, and only a few minutes out of the hours you'll be playing is non-gameplay.  The art and sound contribute to this, with only black and white (though with some cool stylistic tricks), little audio, and no music.  From the title screen to the credits, the game has a definite creepy sense of style that pulls you in. 
 
However, once the game is finished, I found myself thinking that the whole experience was lacking.  From a gameplay perspective, the game is extremely short, and this leaves little opportunity to really develop the puzzle and platform mechanics.  While both are well polished, they just seem under-utilized, and there's nothing that terribly difficult.  Each mechanic gets about 3 or 4 puzzles, and that's it.  And considering the fact that Limbo isn't really doing anything revolutionary in terms of gameplay (Braid, Portal), the shortness of it really sticks out. 
 
Similarly, the story and style are both striking, but each feel shallow.  The complete lack of any attempt to develop the story just doesn't work that well.  There's just a few creepy setpieces along your puzzle path and then the ending.  You're left with a lot of questions, some raised by the game itself, but the game does very little to provide you with any answers.  I was curious to learn more about the other children, the animals, the brain slugs, or even the world in general, but the game provides nothing about any of these beyond introducing them.  And so in the end they just feel like gamey puzzle mechanics and obstacles, instead of parts of the world.  We can debate the significance of various parts on forums, but there's just not enough meat there to really get into it. 
 
I'm glad I played Limbo and I had a great time playing it.  It definitely has a vision, even if it didn't work entirely for me. But it almost felt closer to a deep flash game than a retail $15 XBLA title.  And I doubt I'll be playing or thinking about it much more.  If what you've heard and seen about the game intrigues you and you have some points, I'd check it out.  But (as much as I hate the idea of "more hours == better") there just isn't much bang for your buck here.