Whether you love or hate the prequels, what they did have was a strong plot - the gradual rise to power of Palpatine, the fall of the Jedi order, Anakin and Padme's tragic love affair, and the setting up of the rebellion.
TROS had no plot. In a nutshell. As everyone here knows

I'm a very big Kylo/Ben fan, and was aware of his ultimate fate thanks to leaks, and although terribly disappointed I still decided to see TROS, but half an hour into the film I just knew that I wasn't going to like it, and not just because of the ending.
I knew after thirty minutes it was going to be a bad film, but I didn't realise just how bad.
Palpatine's return was so badly handled it threw me. Snoke revealed as a clone was ridiculous.
The dialogue was poor. Some of the acting was half baked. Leia was demonised. Why didn't she train her own son when she was capable of training Rey? It made her seem like a horrendous mother. Rey and Kylo's repeated fighting was tedious; we'd seen it all before. Poe was completely retconned and the way Finn ran around screaming for Rey all the time was profoundly awful. Then we had a story that kept changing, and the constant 'false surprises' - we are led to believe Rey had killed Chewie, which was a genuinely unexpected shock, then it's 'oh, it's ok, he was on another transport ship we previously saw no sign of.''
Worst of all....Rey was elevated to goddess like levels and her character was an embarrassment. Every other character was rendered unnecessary because Rey was good at everything, plus being so wonderful even Zorri Bliss adored her even though she knocked her on her butt at their first meeting.
Three years later, and I still can't believe they ended a nine film saga with such an awful film. I don't think I'll ever be able to accept it.