She should at least be able to show what the character is feeling. Where was the wide-eyed fear hardening into resolution when she cut herself to distract Victoria? Where were any other emotional transitions? She just looks pissed all the time.

Bella is about as deep as a puddle, but she still feels. Edward has to read her face and not her mind... can he read Kristen Stewart? In Breaking Dawn (the book) Bella becomes a very dynamic character. Is Kristen going to ruin the finale of a good story that has been kicked repeatedly? Most likely. That is because SHE (not Bella) has no depth OR emotional range.