just saying, this was an early sneak peak. And back then, they didnt even have the VHS at home yet so not even could grasp the entire lore yet (which Im guessing is why people kept going back to see them in theaters). A lot of Darth Vader was still shrouded in mystery.
when James Earl Jones first read the script, at the I am your father scene, he thought Vader was lying, as if he was just saying anything to bring Luke to the dark side. And I wouldnt be surprised if a lot of people thought this because the ending was so mysteriously foggy