Woah! I really had a blast playing this! It feels so fluent and looks so neat and cute!
A couple of things I noticed though, was that sometimes the tiles glitched a bit, showing white vertical stripes in between. This could just be a bug on my side, but I know that can be caused by pixel interpolation, which can be either turned off or prevented by giving your tiles a small 1 or 2 pixel "border" outside of their normal boundary. And one other thing I noticed was that the music, when looped, stopped for a short moment. This can be prevented by using cross-fading and maybe different file formats (.wav files, for one, I believe always have a slight fade-in fade-out effect, so then you'd be better off converting it to .ogg's for instance). But these are like minor, technical details (which may just all be caused by my set-up, web applications tend to have such stuff).
But man, did I have a blast playing this! It's really well put together, and I dig the design! Really, great job, especially given the short timeframe! How did you get the music like that by the way? I love it.