This game sure is fun!
I really like the graphics, animations and the gameplay in general.
There are just a few minor things I'd recommend you to change.
After I first started the game and played through the tutorial, I (somehow) confused the logo on the bottom right with the play button...I mean it reacts to the mouse, so... may just be me being stupid though... probably actually.
I really liked that I could preview the whole song before playing. The songs are pretty relaxing and slow (in a positive way).
I, personally, believe that health bars in rhythm games are unnecessary since it's just frustrating, prevents me from learning harder bits by just making me repeat the parts I already know and there is a rating system anyway.
The slight background story is great! Especially how the words show in rhythm to the song.
You probably know this already, but there is no need to hold long notes and for my taste there is a bit much screenshake.
Overall, I really enjoyed my time with the game and will be looking forward to the steam release!