Not worth the $15 at all, the people I know who bought it said it was very short
...zero remarks on the quality of their experience though, eh? Are you leaving that part out? Did they (or you?) not play Portal? Was that a waste of time and money because it was "short"? Portal is similar in length and price if you really want to (unfairly) break it down. I think Portal was initially $20 when it first came out when purchased outside of the Orange Box compliation.
Well straight up--Limbo is a really fantastic game. I love it because--while it tries to tell an interesting and interpritive story--at it's core it never loses sight of what it really is --a video game. It does many other things really well, but the confidence shows through the gameplay as your push through its puzzles.
The platforming mechanic has been tweaked (seemingly) to perfection as it renders a responsive and fun feel for the player. The interface--or the lack there of--doesnt feel contrived because it's never needed. This sort of speaks to the preceived minimalisitc design philosophy of the game that, at times, screams out at you through the missing HUD.
At the heart of the gameplay are the environmental puzzles and it's here where the game really shines. To me, the parts in Limbo that make the player stop, look around and really think are the most important. These situations initially seem dire, but I found that they always had a practical solution in the end. They just made sense once I figured them out (I should probably be clear here and say that the puzzles make sense in the context of the world in Limbo.)
But you see that's just it!
Limbo does a fantastic job of making you think outside of the box without make you feel bad. It's fun, and it does this wihtout compromising itself. Most importantly when you get stuck on a complicated puzzle (and trust me, you will) and then figure it out, you will find that it's always one thing--rewarding.
Look this game isn't going to change your life and I dont mean to imply that it will, but what it will do is create a really fun, challenging and rewarding experience for you for 4-5 hours. That will cost you $15 and it's ultimately up to you to determine if that's something you can swollow. But in terms of entertainment it just boggles my mind that some people would rather pay $15 for a crappy 3D movie rather than play Limbo.