The third level was where the game really shined; when you added in the falling mechanic, I was excited to see what you could have done with it!
^^; And then the game ended.
Aside from that, it's a solid outing save for the menu screens. They seem to be a little wider than 64x64, so maybe try implementing a page-turning mechanic next time, so you can keep to the resolution while still having the full tutorial in there.