It's okay. The protagonist may be appealing to tween girls, but many of the rest of us will find her (and the other paper-thin characters) to be somewhat annoying. The plot is vaguely interesting.All in all I expect the movie may be better than the book, since 2 hours will compress this fluff down into a possibly-entertaining visual experience. 

Question: Why do I have a bad story?
Answer: The protagonist may be appealing to tween girls