Vital parts of the book were left out of the movie. And then they went ahead and made new stuff up. That doesn't make sense to me.
Key characters, such as Luna and Neville, are basically walk-on roles in this film. Ginny is there as a love interest, but she is diminished by their treatment.
What is the likelihood the Weesley's live in the only corn field in Britain?
And how did the Patel twins become white, and what were they doing in the Slug club?