Thank you! I really appreciate the feedback!
To be honest, there was a counter for enemies, but it wasn't working properly (hell, even the counter that is supposed to stop the game from spawning too many enemies at the same time isn't, hence why it becomes laggy after a while) and I was out of time so I couldn't fix it and deleted the code. I do think that would have been good though.
The feedback idea is a really good point. I will keep that in mind.
As for sound, my original idea was to have the game be responsive/follow sound and music (hence why it is called anxious rhythm). Attacks would need to happen in a rhythm and the colors of the level would change in sync with the music. That idea died when I realized I wasn't even gonna have time to get sound into it though.
All in all, my biggest problem here was time management (most of my time went into making the main characters sprites and animations when it should have gone into the game loop) and underestimating how much it would take to get even the basic mechanics to work.
I might go back to this project and try to implement my other ideas later, but I would likely start from scratch if I do, so I can make a consistent art style and avoid the mess I did on the code this time around.