I couldn't take it. I quit after only thirty minutes. I quite like Love Live!, although there are better idol anime. (THE iDOLM@STER, for instance.) Here, though, I had problems.
Firstly, I couldn't remember the characters. It's only been two years, but no one jumped out at me like Nico when I recently watched an OVA with the original Love Live! girls. (Sunshine!! is the sequel.) What I got from this was:
1. an annoying girl who says "zura" at the end of her sentences.
2. a hammy chuunibyou (Yoshiko) who's vaguely filling the Nico role.
3. occasional dead eyes that made me wonder if this was cel-shaded CGI. (Although, in fairness, Yoshiko later gets a comedy facial expression.)
4. Mari's language-swapping, which is grating but not a film-killer. That would be her nuclear apocalypse of a mother, who talks as below and made me turn off the film. Bang. Just like that, out.
"My dAAAAughter ga itsumo o-sewa ni natte orimAAAAsu. Ohara Mari no haha, Mari's mother dEEEEsu!"
This happens quite often in anime. The producers want to flag up "this is a foreigner!", so the character will deliver flawless Japanese in a gross accent and stud it with English words that the audience will know (e.g. "daughter", "mother").
If you speak both languages, though, the character's being a twat. That's business-level Japanese. Mari's mother could get an executive or customer-facing sales job with her language skills. She's so strong that she doesn't slip into her native language for the difficult words... but instead keeps doing so for the easy ones, all in an accent you could use for pest extermination.
The plot seemed straightforward. One of the first things that happens is a five-minute musical sequence. That's not an idol stage performance, but a Disney musical sequence with everyone bursting into song while music plays on the soundtrack. That's the only music you'll get here for a while. After that, we hear about the third years leaving Aqours and see six girls going off to another school. Confusingly, those six are the remaining first and second years. I guess their school closed down or something. (I probably should have remembered, but I didn't.)
Later in the film, apparently they visit Italy.
One day, I might try to watch this again. If I ever rewatch Love Live! Sunshine!!, this is its capstone. I'd definitely have enjoyed this more if the cast were fresher in my mind. Besides, Sunshine!! was charming in Season 1 and still likeable in Season 2 despite losing direction somewhat.
For now, though, it's not for me.