Bay directed both the first Transformers film and its 2009 sequel Transformers: Revenge Of The Fallen, the latter of which was panned by critics upon its release.
"The real fault with [Transformers: Revenge Of The Fallen] is that it ran into a mystical world," Bay explained to Empire. "When I look back at it, that was crap."
Bay blamed the writers' strike for the sequel's poor storyline, claiming that it meant that the film's script had to be rushed through.
"It was just terrible to do a movie where you've got to have a story in three weeks," Bay continued. "It's a BS way to make a movie, do you know what I'm saying?"
The third film in the franchise, Transformers: Dark Of The Moon, is due for release in cinemas on July 5.