The OT seems like generic random nonsense without the prequels. Still good movies, but disconnected. Vader goes from a mildly concerned calculating mad dog, to a ruthless level headed cold blooded killer who is randomly the hero’s dad, and then he is suddenly a conflicted tragic villain. The inconsistency doesn’t make the most sense on it’s own, but if you watch Revenge of the Sith you see him embody all those traits, and understand why he wouldn’t care about the Empire until he meets his son, and why he would still feel conflicted about something he isn’t invested in… Because he’s been hooked on career performance his entire life, hence his Episode IV characteristics.
He’s been placating his guilt for betraying his friends by committing to a persona of evil and burying his pain beneath a monster, making up for a feeling of lacking control by manipulating the fear in others, hence his Episode V demeanor in response to discovering Luke is Anakin’s son. He wants to convert Luke to evil to validate his own choices and mistakes, and when he can’t he finally sees his choices were always a form of denial of his true feelings, which Luke sensed in him. And together those qualities clarify his Episode VI conflict. There’s a vague arc that seems like wishy washy convenient post plot twist course correction that becomes crystal clear when you see where he came from. It takes something that seems spontaneous and shows how well it was actually planned out.
George would always have to explain the trajectory of Vader’s development, and always said there was a missing element of the originals he wanted have clarified when he was making the prequels. Everything he did with Anakin in the PT was to reenforce the way Vader was depicted in the OT. People thought he was a great villain because he was anything and everything to anyone with a scary design and voice, but George wanted Vader to have a very specific tragedy behind him, and that truly made him the best written villain in a beautifully crafted concrete manner. It’s the exact opposite of how the ST builds off the OT, retroactively making it seem pointless in Episode VII, even trying to make it seem politically incorrect in Episode VIII, and then finally mocking it in Episode IX. Every episode of the PT added to and enriched the OT. I’d consider myself an OT purist, and that’s why I love the PT and hate the ST.