This is really, really good. Especially for a first game jam game. The transitions between stages were particularly impressive.
The player character is very well animated. Good use of color and shapes in the environment.
The levels, despite hiding things from the player and changing mid-gameplay, never felt confusing or frustrating. They are very well designed.
Loved the singing at the end. Fantastic.
Biggest gripe was that it was too short. I wanted more!