There was a lot to like about God Help the Girl but despite a few good individual scenes, but it didn't flow together as a story that well. Maybe writer/director Stuart Murdoch needed more creative feedback and better editors than he got. Certain scenes and characters just show up out of nowhere with little connection to the rest of the story, like the WTF scene of Eve going on a bender with some girl we never see before or since. The main character of Eve was weakly written. Her past and her motivations were vague. The movie would have been far better with James and Cassie as main characters and Eve as a side character.
You could see God Help The Girl as a culmination of Belle & Sebastian's (a band named after a fictional band that Murdoch's songwriting centered on) characters and themes spanning their nearly 20 years as a band. James, Cassie and Eve seem derived from the archetypal characters from B&S's songs. The movie though develops them in a shallow and haphazard way that doesn't really do justice to the insights and characters brilliantly explored in the individual songs. I think Murdoch could make a good movie, but God Help The Girl was just so-so. The music was excellent at least.