Good game. I like the big selection of sprites and color palettes.
I'm not sure what to comment when it comes to the gameplay because everything seems good to me.
I've found one major issue with the audio. It sounds like some sort of static or perhaps a short portion of an in-game track that keeps looping non-stop and gets worse over time until you go back to the main menu. Dropping the sfx and/or music level doesn't stop the cacophony either. It doesn't sound intended.
I recorded one level to show the issue.