Excellent job. I'm not terribly good at rhythm games, but the first few difficulties were pretty approachable. Novel idea of using keyboard regions for hitting "notes". I am curious about the actual slap ranks.
Good job on the UI as well, especially with the bouncing text/letters.
I also may have discovered that spamming input has no real penalty besides late or early hits in the end score. I've made an issue on the GH repo in regards to this.
Outstanding, anyhow. :)