I watched them again for the first time recently.

The most obvious problem was just handing the movies over to people with no sort of general outline of how the story should go, just ad lib based on the previous movie. It was a major problem, and is the reason the whole thing was done so poorly.

Secondly, failure to reunite the core group of the original characters for even half a movie was just ridiculous.

Third, somehow Palpatine returned. Ridiculous.

Lastly, turning Luke into a recluse and total failure was a major mistake.

The only really redeeming and interesting character from the final trilogy is Kylo Ren.