I suppose I'm making comparisons that may not apply, but this movie reminded me of another one about a fully insane "pop star" with all kinds of abuse problems. The other movie was much better and the character was more developed. Movies used to be better, didn't they?
This movie seemed pointless, maybe because there was a huge chasm between the young Celeste and the older Celeste. This is where it lost me, because the two seem nothing at all like the same person. It was totally unbelievable, and the narration didn't help and wasn't as clever as it tried to be. I just thought it was awful. That so-called music and her stage act were awful. I'm not a lover of pop music anyway, but this was tripe. There was little meaning to be had, and just watching another movie about a failing famous person isn't all that interesting. Cheap is how I would describe it.
They'd have done better to explore Celeste and her sister's relationship and delve more clearly and deeply into the character. It just flashed past her early years into a full on ugly celeb type movie.
I would throw rotten eggs, not tomatoes.