The fact that Megan Fox wasn't always happy on the set of the 'Transformers' movies isn't a secret. She had a very public spat with director Michael Bay when she quit prior to making the third of the films, claiming that he'd been abusive towards her. That may have soured her experience of the entire franchise, although based on earlier interviews it seems like she never thought all that much of them anyway.
Speaking at a press event before the second movie was released, Fox said that 'Transformers' films weren't really about acting, and that they're essentially just a series of action set-pieces. Elaborating on the point, she said that her part generally involved either running, screaming, or both, and that she knew she was largely just there to look pretty. We think it's safe to say she'll never do another one.