Cool, The Idea is really great.

The Enemies have a bit to much Range in my Opinion. But there could be alot of variation with more Instruments, different Ranges, different Beats.

I Also would change that Circle maybe to a Endless Bar on the Top where you have to hit the Notes right in the Middle  instead of that Circle which blocks Vision and Confuses and feels not so nice.

So its out of the Way, not blocks Vision and its more Clear where u at, because in the Circle i really loose Track of there the next Nodes are coming while the enmies around me.

Good Work anyway!

The game is fine, but the tutorial just confused me.

Perhaps it can be polished even more so that it feels better and the state of the game is more evident. I like what you've done.