I liked it a lot, but didn't love it. To me, it's a film that suffers from really mixed messaging.
The stuff just focusing on Mei having to deal with being a thirteen year old girl is great, and it's honestly fantastic that an animated film has finally been able to address female adolescence in a way that's honest and funny.
However, the film also suffers from a weirdly pro-capitalist theme that undermines a lot of the more positive stuff. If the red panda is symbolic of Mei having to deal with adolescence as a thirteen year old girl, then having the main story arc centre around Mei's friends encouraging her to let other kids at school touch her, film her and invite her to parties in exchange for money is just... What?
Or the way that Mei's family try to use "traditional" (within the context of the film) Chinese methods to contain the final threat, but are unsuccessful in doing so until the manufactured American boy band decide to use this as an opportunity to shill their latest single, which then saves the day.
Or the way that Mei's family temple in the ending is literally turned into a merch stand where visitors can buy red panda t shirts, red panda lunchboxes, etc. And the film sells this as a good thing.
There's a really good film about being a teenager in there, somewhat smothered by what feels like a weird bit of corporate apologia.