The premise is really cool. I don't know why they decided to barely do anything with it and instead just went the "erm what if Undertale was evil?" route.

You barely get to know anything about this world or any of the characters.
The plot is so cryptic and confusing, and it feels like it's leading up to some huge final twist that never comes.
The ending basically boils down to: "We didn't want to die, but now that you killed us, it actually ain't all so bad :D also Buddha is here)

And then the big emotional sendoff doesn't feel earned at all, since this game is barely 5 hours long and only 2 of the ~30 characters have any semblance of a personality. Do you really expect me to care about the save lamp posts? The mushrooms that have one line each? The purple haired lady?

Most of this game feels like a checklist of cool ideas the devs had, but none of them are developed very well:
Musical battle system ✓
Psychedelic gnome sequence (pretty colors) ✓
What if the castle was actually alive?? ✓
Spooky maze with chasing monster ✓
Mario Kart!! ✓
Rabbit = Sun ✓
D&D sequence ✓
Walking through a desert (cool 3D effect?) ✓

The sequel's gonna have a slime girl though.