I never turn off my brain while watching anime, except for this one, and even then I didn't enjoy it.
The Art Style is outstanding, it's beautiful, but it is all useless because the anime in itself is bad.
The characters are annoying, the plot was so bad I hard guessed it on episode 4 ... episode 4 out of 22 !
Also I hate the fact the MC can't stop about telling us that ''Urr Durr I express myself through music, but when I'm playing it I can't stop from having an internal monologue that mostly won't make anysense and where I'll repeat myself a bajillion time'', and I was like, Ok if you talk through music, then ... let me hear your music you dumb ersatz of a MC.
Then the ost was kinda good, but it was not enough, coming from a music anime.
So overall, an overrated anime that even tho it talks about music, doesn't let us enjoy it, which is a bad side since it's the only thing it's got to it.