Nice work, it's pretty well polished. I especially like the musical notes when you change size, and the little cloud puff when you zoom by when small.
I found having to slide the bar, while using my keyboard keys to move a little unintuitive. Perhaps finding a different way for the player to control changing their size (such as q/e) may help the usability a little.
Also appreciate the inclusion of a tutorial, that's always nice.
Good work.