After Earth & The Last Airbender have to figure prominently into this discussion. They are both slick big budget films that clearly aspired to be multi-film franchises and they not only fell far short of expectations (particularly TLA because it has such beloved source material) but they were simply terrible films. Bad story telling, bad acting, bad everything. I would have no problem listing these two among the worst ever.
And as a bonus they were both directed by M. Night Shamalammadingdong. There is no way this guy gets another big budget film green lighted, it's a shock that he has managed to finagle two films at all considering these were his two previous films.