I love the visuals.
I'm kinda confused what the difference between the reset and stop buttons is, both of them remove all your notes. The controls feel a bit clunky for someone not used to playing keyboard.
As a general rule of thumb, remember that in games, the difficultly should be figuring out a solution, not inputting it. Making it difficult to input solutions once found makes the game significantly less accessible to the disabled and frustrating to everyone.
The player just kind of gets dropped in without any idea what to do. There definitely needs to be some level of tutorialization.
I think it might help if you had a record mode where you could just input notes as it loops so you could do part of the arrangement every loop, the reset button would clear all of your notes, and a play mode where your character is actually spawned in. Something that invites the player to actually start moving.
Fantastic art. Cool concept. The UX is just a little rough. Overall, good job.