I don't like Enzo, nor do I like Bonne with Enzo. In fairness to Enzo he showed up too late in the series for me to care about him, but they should have put Bonnie with someone we actually cared about. Bonnie/Kai had fire chemistry though.

Only a hot take depending on who you ask, but Stefan/Elena should have been endgame. Once they knew Nina was leaving in s6, I don't care if they rushed it, it would have been much better.

They went too far in making Damon and Klaus bad and then trying to redeem them. Like Damon killing Jeremy and Klaus killing Tyler's mom. Just getting rid of those two things would have made those characters a lot better.