I like it, there's actually a lot of different mechanics crammed into this game, and some levels are designed pretty well.  I especially like the level where you're trapped and have to jump immediately with the exit right in front of you, but because there's a gravity crystal in front of the door, you've got to go all the way around to come back down (a lot like Veni Vidi Vici from VVVVVV, but a lot less cruel).

I do think though that this is a game that would've fit better in last year's jam, which had the theme x genre without y mechanic (in this case, platformer without jumping).  Mostly because the one jump mechanic is only a small part of the game, a small puzzle of "Where do I jump?" where the solution is usually fairly obvious.  I think in most of those places you really could have just had a spring and it really wouldn't have affected the game all that much.  To design around the only one mechanic, one possible way would be when you jumped, you lost your shoes, and then you had to retrieve them to jump again, and then you could design puzzles where you have to return to previous platforms after hitting switches and the whatnot, or conveyor belts move your shoes to new locations or other mechanics.

Actually though, I think if you wanted to take the game further without changing much about the inner code at all and just designing more levels, I think it would be best to give the player more jumps.  Obviously, that now wouldn't fit the theme, but it does let you have more interesting puzzles where the question of "Where do I jump?" becomes a lot more of a challenging question.

Still, I want to reiterate that I did like the game, the puzzles were good, and the mechanics were probably more than I would have expected in a game jam game.

Nice concept. With some interesting levels it can become something pretty cool :)