I don’t know if these listed are controversial. If anything, they’re pet peeves of mine.
Count Dooku using Sith lightning ruined the prestige.
“Who talks first? You talk first or I talk first?” is a more out of place line than “Ouch Time” or “Do you want to buy some death sticks?”.
There were too many Jedi in the prequels, which watered down their lore. I find it hard for Palpatine and Vader to fear a Jedi destroying them both when a battle droid and clone trooper could take one out.
Obi-Won’s “true from a certain point of view” explanation still felt like a retcon.
Darth Plagueis wasn’t that wise.