I didn't play it long, but I certainly enjoyed it.
The concept actually seems like a really great one, and unlike a lot of the other people here, I think the game doesn't need a whole bunch of upgrades, just some levels or even a separate game that focuses on this concept, because it feels really good where it is right now.
No major issues with the game except the camera is a little shifty when it's in the air, or you're moving from platform to platform.
The ambient noise, while it may have been pretty simple, matched with the game's already simple feel. Maybe music would've improved it, maybe it wouldn't, but you're certainly not doing anything wrong with it right now.
Overall I think you've got a really good concept here, and its execution for a 72 hour span is quite good. It may not hold interest for very long, but its basic play is good while it lasts. Maybe it's odd to think, but I'd be really interested to see a full, progressive game made like this.
The camera issue just barely knocks this down to 3.5, but if that were fixed, then I'd have to say 4 stars for a Ludum Dare game.