I like the Gravizando mechanic, and having it be placed with the mouse cursor really helps with making things feel just about manageable. The melee attack felt a bit off in terms of the hit boxes, and I had to learn to stand further from enemies than I originally thought I needed to.
In terms of the music sphere that's being attacked, was there a way to see how damaged it is, or how close it is to being destroyed? I thought it was indicated by the note type, but below I see you mention that it indicates how close you are to getting to the next stage (a very cool indicator, by the way!).
Overall, it was a fun game, though I got overwhelmed when the slime guys started showing up!