it's been done, and that's ok
Making ‘unoriginal’ movies (e.g. a sequel or something based on a book, toy, comic book or other pre-existing material) is a way around this, as it encourages people to go to the cinema by saying, ‘You’ve heard of the Transformers and know what they’re all about, so you’re probably not going to hate a movie about them, as it’ll involve robots fighting’ or, ‘This is a rom-com and therefore at the end the boy and girl will get together, so even if turns out that most of the film is crap, you’ll feel happy at the end’.