Now first things first...

This game is not from the same devs as undertale. although it does seem to appear that it was inspired by undertale... the only similarities is it's art style. Other than that it is no where near similar to undertale in terms of actual gameplay.

--How I see it is this... imagine guitar hero except you are moving a character around to dodge and reflect the notes instead. Your character is not in sync with the song, only the enemy shooting the "notes" out is in rhythm with the tune.

--I will leave a disclaimer here for people with epilepsy. This game has a tone of flashing lights and goes hard on that. luckily there is an option to tone this down for people with hypersensitivity issues. This game is intentional on that note to make it trippy and can be very disorienting for some.

--each character you fight is a separate boss with their own unique song attached... there are no multiples of generic enemies to fight in this game. If you are playing on harder difficulties, let this be known. this game can get really hard at times depending on the boss you fight. there will be a few bosses that will make you want to pull your hair out and break your keyboard across your desk. But that makes it all the more satisfying when you do beat those bosses. luckily, none of them use cheap/unfair tactics here.

--there is plenty of gameplay here. It will take you around 4-6 hours just to be at around the halfway point in the game. For the main ending... it can take you around 12-14 hours depending on how good you are at dodging and reflecting notes.
for me as a completionist i wanted to achieve all the endings.

--there are three endings in this game that i am aware of. depending on the ending you wish to play after you hit the halfway point it can take you anywhere between 20 minutes to 6-7 hours depending on the ending you wish to seek.

--every character seems to have their own quirks and are interesting here. for me this story was pretty fleshed out. I had no pacing issues with except with the desert level... I personally did not like the length you had to run just to get to the end. it reminded me of another game just for a second while running *cough desert bus cough*.

--the only thing I didn't really like is when the notes start moving around like a wave. this can be very disorienting for some players.

overall I will give this game a 9/10. It is an interesting approach to rhythm games and the bosses are good enough to make you anticipate the next one. There isn't really anything like this out there that I am aware of. The soundtrack I do believe is near perfection here. there were only a couple songs from bosses i did not like here such as the worm.