Warning: way too long review incoming
Great game, at least one of the best iv'e seen on itch.io. It has some very good design overall. The music is good, the gameplay is also very fun and the difficulty is very well balanced. Hard enough that i couldn't beat anyone first try, but FAR from "getting your head bashed into a brick wall" difficulty. Came inn expecting a full game and was a bit dissapointed when i saw it wasn't one, but it was still very fun as i said.
It could use some details in areas like the club, like maybe the other npc's on the dance floor would change their dialouge after the fight. Also the battle in the incinerator is kinda weird and unexplained. I hope (if kept), that it is explained/fleshed out in a full release.
In addition as mengtioned, the areas like the club could have some more detail and polish, also graphically like adding a couple small details too keep it up with the level of visual polish that the rest of the game has. (at least in my opinion)
The one additional complaint i maybe have is that dying feels a bit wrong when the game just fades away. Some animations would be very nice and maybe seeing the enemies celebrate and stop attacking would help.
Also i hope that this game does not become too much of a meta game like undertale or OneShot. Those games are great, but if this game does not have anything to add to that table, i hope that it instead focuses on a seperate story that is not too "meta" (looking at itself as a game, characters knowing about functions like saving etc.) Maybe something like Just shapes and beats. That brakes a lot of conventions, but still keeps the imersion and doesn't break the forth wall.
Overall it is a very fun, well designed and challenging game. Though it need this much more polish (squinting my fingers with less than a millimeter of space between them). The battles fellt very nice and had a lot of game "juice" and i overall enjoyed this game/demo a lot. I usually don't use rating scores but i would probably give this a 9.5/10.
(also i used way too much time to write this review/comment or whatever, but i hope it helps. Also sorry for my (probably) countless of missspellings. English is not my native language)