Teen Spirit doesn't try to be something it's not. It provides face-value entertainment for 90 minutes.
It's definitely worth watching for Elle Fanning's performance alone.
Acting: 8/10. Fanning is superb (acting, singing and dancing); supporting cast is convincing enough. Plot: 7/10. Good pacing; visual storytelling is favoured over dialogue; average character development; one or two unexpected twists; decent conclusion. Production: 8.5/10. Believable locations, sets, costumes, etc. Soundtrack: 6/10. Notably predictable songs throughout. (Perhaps that was intentional; this is a movie about a pop music contest, after all.)
Overall recommendation: Watch it (once is enough).
Acting: 8/10. Fanning is superb (acting, singing and dancing); supporting cast is convincing enough. Plot: 7/10. Good pacing; visual storytelling is favoured over dialogue; average character development; one or two unexpected twists; decent conclusion. Production: 8.5/10. Believable locations, sets, costumes, etc. Soundtrack: 6/10. Notably predictable songs throughout. (Perhaps that was intentional; this is a movie about a pop music contest, after all.)
Overall recommendation: Watch it (once is enough).