Really cool concept, and quite well executed.
The laser on the boss is way too difficult compared to everything else. I can dodge all enemies, all bullets, but the laser gets me every time given how fast it is.
Lasers aside, the game is very slow, in terms of going room to room, in terms of enemies, in terms of projectiles. I don't really want to replay it when it starts off so slow only to die to the boss despite how interesting it is. I guess I feel like I've seen most of what the game has to offer quite quickly, it's cool, but there's not really any intensive to play more.
Not really sure what the darkness adds, felt like more of an annoyance.
Is the green a dash? Given you already have a dash. perhaps something else would fit better, like the ability to destroy enemy bullets.
Lastly it could do with a lot more kick to it. The rhythm elements have a really great feel to them but everything else is very lacking.