I always thought that ROTJ could have revealed that Vader was lying to Luke, cause that would have been cool. It would have made ESB so much more powerful cause not only did Vader physically beat Luke on Cloud City, but it F**ked him up mentally as to who Lukes father was.
It could have created a great decision in ROTJ for who Luke should trust, ObiWan or Vader? Maybe even ending the saga as Luke kills Vader and we never know if he had killed his father, or he killed the man who killed his father? Just a different twist I guess.
As for all the redemption of Darth Vader crap in ROTJ, and now the full of arc of the PT, that story does nothing for me, SW movies shouldn't be that personal, cause the way Lucas makes the movies, those scenes just come off as goofy compared to the powerful dramatic scenes in SW & ESB.