The movie takes turns making us wonder who we're supposed to have sympathy for and while the more mature leads (Weaver and Curtis) are excellent the final product is an inexplicable mess. I get that there's got to be enough material to stretch the premise out--although one wishes they could've just come up with a meatier premise--but the movie feels unfinished. Perhaps there was some more explanation of Jonna on the cutting room floor? I'm not sure.
Bell is a strong actor and the movie really focuses on its female leads leaving the men in the movie (including an uncredited appearance by a professional wrestler) with very little to do. That's not a criticism: there are plenty of movies that go the other way. The problem here is that the material simply isn't up to the task of keeping us interested--especially if we feel that Marni (the most sympathetic character) is behaving poorly in the beginning and then switch over to feeling confused when new facts come to light. It isn't deft movie making to have the audience sit up and wonder if this is plausible.
If you like Weaver and Curtis it might be worth going to see them together. If you really like Bell (as I do) you might want to just see her. If, however, the cast doesn't draw you, the movie probably won't.