First off, before I say anything else, this game is really high up on my list of rhythm games, and I return to it constantly!
I do have some suggestions for the game, though (QoL stuff, not content):
1. Some more visual and/or auditory feedback for hitting notes (Especially for those notes at the end of Hard Tutorial) would be much appreciated.
2. The note BPM of Week 1's second song feels a bit slow, as every phrase seems to start at the correct time, but slowly drifts away from the actual BPM of the song as the phrase goes on, and then it gets fixed again at the beginning of the next phrase. This happens with other songs, too, but this song in particular is the most noticeable offender of this.
3. There are some extremely short hold notes in some songs that feel unnecessary, and could probably be changed to tap notes.
I don't know if any of these are already in development, but I felt like I would share my opinion anyway. Even if this doesn't help you at all, I still wish for you guys to keep developing this game, as I think there is something really special here.