Nice job with this puzzle platformer! I found it a little difficult to play in a few places, and wondering if these are areas you agree with?
I couldn't see the end door, it was too dark. For the first few levels, I just went all the way to the right, but then one level I couldn't, and I had to really closely examine the level to find the door. Even after I knew that, each new level I had to find the door all over again because I couldn't see it without focusing. The goal should probably be easily identifiable, otherwise players aren't going to know what to do.
The spikes seemed a little unforgiving, as just touching them would kill you, even if it was from the side. This combined with jumps that you can *only just* make was a frustrating combination. I stopped playing after getting a game over (the level with the green and red boxes) and had no desire to go through that all again just to get to that point. Also, learning what the green/red boxes do by dying meant that cost me one of my lives, which wasn't a great way to learn that since I had limited lives.
For a GameJam game, you probably benefit the most if people can get to the end of your game, because then they can see all the content you made. Perhaps consider counting up the number of deaths, instead of counting down the number of lives? That way, no matter how many times people die, they don't have to start again, but you still have a way of players rating how well they did based on deaths.
I like the core of the game, I think it just needs a few tweaks to make it more enjoyable to play.
(-Joe)