It's not a film, in any recognisable sense. It's a live stage concert. I presume the bands and actresses really did a concert for a live audience, then it got motion-captured or something into the CGI anime models from BanG Dream! Season 2.
Result: the film's critic-proof. You're not wearing your movie-watching head. There's no plot, story or characterisation. It really is just 25 anime girls playing music on stage. (Five five-girl bands.) The only possible spoiler would be the set list. Do you like these girls' music? Do you like going to concerts? Are you a BanG Dream! fan? If your answer to any of those is "yes", you might well enjoy this film. (You don't even really need to use your eyeballs... you could just get some headphones, put this on in the background and not really miss anything.)
Each band plays three songs and has a little bit somewhere where everyone says hello to the audience and says who they are. This only lasts a minute or two. Then, at the end, there's an encore from a couple of bands, plus a bit where we're seeing videocam footage and following the girls offstage. (We glimpse people like Rock and CHU2.)
(The songs are a mix of short and full versions, but a bit different from the regular ones. It's possible to buy an album of the film versions of the songs, in fact.)
0 min = Poppin'Party
9 min = Afterglow
19 min = Pastel*Palettes
28 min = Hello, Happy World!, i.e. my favourites. (That's because I find them funny rather than because I have any particular opinion about their music, incidentally. Doesn't Michelle get hot in that bear suit, by the way? I wouldn't like to perform in that in a Japanese summer.)
39 min = Roselia
48 min = Poppin'Party again, after which the girls go offstage, come back on, etc.
Is this film good? Category error. Concept does not apply. I can't imagine ever rewatching it, but I don't mind it.