I like the art and the sound, it has a little retro vibe.
The levels seem a little bit hard, because you have to play almost perfectly. I would give an extra time freeze to every level to let space for some errors.
When there are shooting enemies, they can reach you at the start, I would give them range, because it's frustrating to die if I don't start moving instantly.
These are mostly level design issues, the game mechanic is interesting.