Consider this "What If..."
The Empire Strikes Back hits theatres in 1980, and a certain very famous scene goes something more like this...
Vader: "Obi-Wan never told you about your father did he?"
Luke: "He told me enough. He told me you killed him!"
...
Vader: Perhaps I did, but only for my survival. I was not after your father, Skywalker, but was rather seeking an escape from the confines of the cruel Jedi Order. Your father pushed Obi-Wan to hunt me down, and the two of them duelled me over a nuclear reactor, where I fell, but not before slaying the esteemed Skywalker, who wanted my death...who was jealous of my growing power. I was just a boy then, Luke. A boy like you, but they wanted me dead.
Luke: It's not true! It's impossible! Obi-Wan is a great man! He and my father were great Jedi Knights...they fought in the Clone Wars...they...
Vader: Held me back. And were as unwise as they were old. Now they are the ones who are gone, and I rule the Galaxy...or at least I will, once I slay my...new master, as I did to my old teacher. Join me, and we can rule the Galaxy as the two last surviving users of the Force...once we have rid the Galaxy of the Emperor.
Luke: I took an OATH...to the Jedi and to the Republic
(Luke falls down the shaft...realizing Vader offers nothing but evil ambition, and goals of galactic domination...the ways of the Dark Side...)
My above "what if" scene incorporates elements from an early script treatment for ESB, where Vader was not Luke's father and where Luke met his dad's spirit earlier on Dagobah with Yoda, where he was sworn in on the Oath of the Jedi.
Would ESB still be a great film without its thrillingly great twist ending? Would it have changed the course of Star Wars for the better or worse? Would it have made it so the original Star Wars was let ret-conned? Or would it have made for a thinner saga?
(Please excuse the bad dialogue in my "what if" script lol)