Let me start by noting that the resolution of this game is pretty large and I could just barely see the bottom of the screen with my small 1366x768 monitor. For accessibility reasons, it would be nice if you had the option of choosing a lower resolution
I quite liked the song and the art style and basic gameplay seemed to work decently, but in my opinion, for a rhythm game, you really need to have clearer tells when "notes" are going to drop. Right now, the small black things in the center of the spawner are only really noticable when you focus on that region, and since humans can't focus two things at once, it means you'd constantly have to redirect the focus to catch everything, which just isn't very fun. It doesn't help that the background is so flashy and took up quite a lot of my attention.
Also, I think there needs to be some sort of punishment for reaping nothing. Right now, I found to be much more successful if I just mashed both mouse buttons in succesion instead of trying to hit the actual notes.
Since you seem to be still actively working on the game, I think you could make it a lot more fun by only making pretty minor improvements. Mainly by making a much more noticeable tell for when notes are about to spawn.