The music was fun and relates well to the aesthetic and the kind of game this is.
The UI wasn't as bad as you said in your description, the only thing I would say is that the buttons should be a bit bigger, and the UI should have a bigger presence on the screen :)
I liked the concept very much. Some levels were, as you said, challenging, and some were a bit too complex at first sight (but once thought through, each level makes sense)
Well done!