Love the concept
I just love the concept of having one thing that you control suddenly morph, and the whole world just change around it, like it does in this game. I had actually been planning to make a game with such a concept myself. The art in this game is one of it's best features. It was really well done; I would have liked to see it at a larger size though. The resolution of the flash is a tad small and looked like it hindered the showcasing of the art here.
Something I would like to see though having the fighting mechanism tweaked or changed during phase changes. It was nice to watch the phases changed, but just that; I could have watched them and listened to the music without tapping the space bar and arrow keys. If there was a rhythm I should have been doing it in for a better score, I was not aware of it. If there wasn't, I really think that adding different gameplay mechanics and sound effects would have given it a lot more depth, though I realize you didn't have the most time to develop it.
Overall I think it's great.