1) Star Wars
Star Wars fans have often disputed George Lucas’ claim that he had at least the original trilogy, and possibly the prequel movies, planned out from the beginning. The biggest piece of evidence that proves he didn’t is the totally different first form of the film that would become known as Episode IV: A New Hope.
Called The Star Wars (and before that The Journey of the Whills), it followed a petulant teen named Annikin Starkiller as he’s trained in the ways of the Jedi by General Luke Skywalker. Han Solo and Chewbacca are still around, of course, but they were depicted as a green-skinned alien and a scary-looking ape creature, respectively. In one memorable scene, Annikin would have punched (the 14-year-old) Princess Leia in the face… which then led her to fall in love with him.
Clearly, the basic shape of the saga was there but most of the elements that made Star Wars so brilliant were not yet in the right shape. We’re not sure we’d be getting The Star Wars: Episode VIII at the end of the year if the original movie had been made in its early form.