Not bad. As mentioned earlier, there are some physics issues, i.e., you're stuck when you land on the ground until you jump. I also found that the jumping was unexpectedly high, which was perhaps the point, but given some of the entities you played as I didn't understand why some of them could jump so high. The visuals are simple and cute, although I noticed in the 3rd level the frog blends in a bit with the green part of the background, so at first I couldn't see where it was. I'd suggest more contrasting shades of green in that regard. The music is alright - admtitedly, after the 10th or so loop, it began to get a bit irritating.
It indeed was unexpected to play as different entities, as going into this game I thought I would primarily be a frog, but it was a welcome surprise.