Played this on Twitch yesterday.
Had a great time loosing it while playing. Love the graphics and audio. The fact you can simply refuse to play the game at the beginning point blank killed me. Really liked the idea of using a stack of power-ups as the health system. IMHO where the game fall short is on how controls feel. Having tight and enjoyable platforming controls is really hard and for me they aren't quite there on this one. It feels kind of unreactive on the X axis and too reactive on the Y axis, resulting in most jumps being a tad awkward. More air control would be nice too. And obviously gamepad support would help a lot.
I'm a fan of the fact you can play the levels as you want in no particular order. That way you can just decide one level is too hard and continue on your merry way. Well... You could do that if there was a way to back out the levels, but you can't. So once you're in a level you can't beat, you're basically soft-locked and need to reset. Which defeats what's nice about not being forced to play every level. But I imagine it's more of a jam oversight than anything.
Anyway, I'm rambling now. You made a cool game. Go over and smooth the controls, give the player a way to exit out of levels, and it'll be even cooler! Keep up the good work!