Really nice!
Just some issues: When u restart a level, it s not entirely clear when exactly it starts, causing you to run into spikes quite often at the beginning of a level ( happened to me a lot in the last level) - a "GO" sound could help so u know exactly when your controls are free for you to use.
Add level numbers, so we can give detailed feedback about where and when a bug occured. I had one, for example, but i cant tell you which level it was in because there was no level number:
When I jumped onto a "black hole" block (the one which cannot be exchanged) and tried to change a coin block with an earth block, I fell through the "black hole" block. This happened multiple times. I remember, there were two coin blocks to the left side of the position where i stood.
Controls: Maybe a frame for movement acceleration would not hurt, to let us turn around without moving, in order to face a block on our left side without touching it. Also I often ran into spikes because I could not fit through a 1-size-gap, for the character moved a bit further than I wanted him to.
I turned the music off after 10 levels, that s something I usually do not do. Must have annoyed me for some reason, I think the peaks of the stick-drums were to high in my ears.
Good game still, after all ;)