Prequel Obi-Wan is a bad person, his character is written inconsistently, and he’s overrated by fans. I know the whole “He mutilates Anakin and leaves him to burn to death next to a volcano” was something George had come up with a long time ago. It’s still stupid, though. It goes against Obi-Wan’s character, and it doesn’t make sense with the tone of their reunion on the Death Star.
Qui-Gon Jinn should never have existed. His existence contradicts what’s said in the OT, he takes away screentime and development from Obi-Wan, and because of him, Obi-Wan lacks agency since he only trained Anakin because Qui-Gon told him to. The fact that Qui-Gon is basically the protagonist of the first film of the prequel trilogy was a huge misstep.
Prequel Palpatine was excellent until halfway through RotS. Before that point, he was really well acted and his evil was subtle and sinister. Palpatine in the second half of that movie was a clown and ruined the intimidation factor of the character.
(Maybe these aren’t unpopular opinions on this site, but they are unpopular elsewhere.)