Great job! Reminds me of flash games I used to play when I was a kid. There were certain forms I found more useful than others but I think you can use any form in most levels and I really like the open-endedness of that. I got stuck in a few parts but trying different combinations of forms kept me from getting too frustrated. I also really liked the little text accompanying me through the levels. Its the little playfulness that gives games like these so much charm.
I enjoyed the music, especially after it built up, but I feel that it should change to something else after it ends or loop instead of just staying silent after. Also (not sure if this is a glitch or not), but it would be nice to have at the least a little ending slide after the final level. For me, it was just a dark blue background.
Overall, I really enjoyed it. Good work. :)