Just finished playing your game. Super impressive stuff! You chose an aesthetic (retro/pixellated) and stuck with it throughout. I thought that this elevated each individual piece of your art/UI design.
As far as gameplay is concerned, I liked that each animal controlled differently. Particularly cool were changing from the swimming tadpole into the hopping frog and the snake wiggling.
If I had to give one piece of feedback, it is that I think that the gameplay in general could be sped up a bit. This would make eating everything as a snake or running around as a grasshopper a bit more exciting.
This is a very solid base of a game. If you wanted, the fun factor of the game could be lengthened by adding more objectives for each animal. However, I did have an enjoyable time just trying out the different forms. Nice job!