Gaffer Tape said:
See, I disagree because Return of the Jedi ISN'T about Vader, again, despite what Lucas would have you think. It's about Luke and his internal struggles. His desire to bring his father back to the good side. Because of that, it's what we know about Luke that's important. We don't really need to know about Vader or the Emperor beyond what we get in ROTJ to understand their relationship, and, more importantly, Luke's relationship to both of them. In earlier drafts, Lucas did have more backstory and more scenes with Vader and the Emperor, but those were ultimately jettisoned because it needed to be more about Luke, and because those scenes tore down Vader as a villain and made him too sympathetic. If we know too much about Vader, and he's made sympathetic, then whether or not he will become good becomes a non-issue. Luke doesn't know for sure; therefore, we don't need to know until the moment that he does.
I'd add that the OT already adds too much confusion as it is.
In ROTJ, it appears as though the Emperor has Vader completely enslaved and on his knees with a dead spirit.
"You have no idea how strong the dark side is; I must, must obey my master" sounds either like he'd be horribly tortured if he stepped out of line, or as though he had no will of his own, basically being "compelled" and "addicted" to obeying the Emperor no matter what.
Or maybe the Emperor would threaten to use some Force thing to draw all emotion out of Vader and cast him into wailing and despair?
Vader's "awakening" at the end seems so much more significant, and brave, in that context.
However, not long ago, in the previous movie, Vader was all talking big about overtaking the Emperor with Luke's help.
So there, he takes out the Emperor, why is he now suddenly good?
Then comes ROTS, and what we're basically told, is that Anakin simply sticks to Palpatine, because he thinks this is the right way to go for the galaxy, or because, well, he's done a lot of crap and now he's just stuck with him. Maybe grows more cynical over time.
Maybe needs someone to fill the void left by Padme, har har har.
Or maybe he feels gratitude for Palpy for restoring his limbs, and/or at least trying to help him with Padme's death?
So after all those years of badassery, he's still completely duped?
So that's just the final nail in the coffin.