Hey,
I feel the idea behind the game is solid. There are however couple of things that I think could improve the experience:
1. The length of cutscenes is definitely too long in comparison to actual gameplay time. I spent probably 2 times more time on reading the dialogues than playing the game.
2. There is no clear indication "WHERE" is the sweet spot for pressing the button. I realized that it is close to the end of the screen just before the first song ended.
3. The level of the songs is a little bit "too hard" for a such a short game. I mean, I managed to pass the game but I completely did not get a feel of the songs - I felt more like I am bashing my keyboard. I think game with this type of mechanics would benefit from slower songs at the beginning.
4. The feedback of 'well pressed button' should be more visible. You can see good execution of feedback in games like OSO! or Saber Beats :)