Hi! I've only played the demo but I like the game a lot! That said I have a few concerns...
-The visual polish is great (personal preference but a majority blue UI kind of makes the colourful characters feel flat... thought not an issue I think would be shared by many) , but whenever a slider pops up and I'm in the zone I kind of miss it a lot of the time because it is kind of just lighter blue on blue.
-The music is amazing but the speeding and slowing mechanic is kind of jarring for me? I'm not sure if it's preference but when the meter fills up and the music slows down I tend to miss the next note or so because it messes my timing, same for when it speeds back up again, maybe if it were a toggle or something it'd be ok?
-While I understand the levels are procedurally generated a lot of the beats feel very random? It doesn't quite play like a rhythm game in that I can tap to the beat (which does work to some extent) but more like me watching the bar and guessing when I should tap it.
-This last one could be completely unfounded if you can change settings in the paid game but cramping the buttons to only the arrow keys feels kind of clunky. Not only am I forced to fit all my fingers in one area (considering I'm playing it with 2 hands) but also it actively encourages one handed play, which may work for some people but coming from other rhythm games I find being able to divide my attention over the keyboard more comfortable and easier.
With that said I see a lot of potential in the game! I'm not a game designer so I don't know these mechanics all the way through, but I would love to see where this can go next!