Top marks for presentation. Great music, beautiful environments. The main character is well-animated, and the character controller is superb: the slime handles like a dream.
I see that some other players had difficulty with the wall-jump. Although this is usually a feature I don't really like in most games (grrrrr, Ninja Gaiden), here I thought it was implemented cleanly and didn't give me any problems.
My main gripe is that even the weakest enemies are in fact very tough. Those little gremlins take several hits to defeat, and they attack with a vicious combo. The first enemy in the game should not be this aggressive. :D