I really like the graphics and music but I wish the gameplay didn't include shooting and was instead about jumping, sliding under obstacles (held notes that are longer) and stopping to avoid falling debris or something (short pauses in music). As mrmatt said, it's pretty dang difficult to be looking both at the ground and aim your mouse at the same time, especially at the scale we're talking here. Or maybe I just suck at these kinds of things (I do).
If you get a chance, please check out my entry.