This is a cool interpretation of the theme. I like the idea of firing with the rhythm. It's always cool when games sync to the music. I also appreciate the unique interpretation of scale as a musical scale. The UI for the pulsing circle inside the cannon is very well designed. My biggest point of feedback would be to make the enemies a bit more threatening and/or reduce the size of the arena. I would also suggest breaking your combo if you click with the wrong timing so you can't spam.
But overall, good job!