7. Close Encounters of the Third Kind
Though Steven Spielberg was one of the very first filmmakers who publicly took to making a big deal out of going back and re-touching his films, he's also one of the most infamous for making changes that haven't gone over too well with fans, and in the case of his Special Edition of Close Encounters of the Third Kind, even ending up regretting it himself. The key mistake is showing the inside of the mothership and having Richard Dreyfuss actually see the aliens, though this was apparently part of a deal that Spielberg made with the studio, who only granted him money to finish his new cut of the film - as he was extremely disappointed with the theatrical cut - if they could use the mothership scene as a marketing gimmick to hook the audience. In other areas, the cut is actually superior to the theatrical version, running three minutes shorter and cutting a lot of extraneous material, but the mothership scene is simply too much, a result of studio greed, and when Spielberg later created a new cut, he decided to omit this scene.