Impressive amount of work done in a short amount of time! I agree about feedback, I got to the final boss but I didn't defeat it, mainly because I didn't know if anything I did was actually working!
Also, while the visuals are good for the most part, I think some blocks are too similar (Like the arrow and spike block, when I'm zooming through a level, I just see the brown block!). Also, and this is pretty nitpicky, but the health bar, while looking nice, sometimes got in the way. I think that a smaller health bar would have been just as effective!
Still, really impressive to get so much done in such small time and resolution!