I don't think many of us "hate" ROTJ. Personally I find it suffers in comparison to the first two in a number of ways:

It feels like they're going through the motions. Lucas seems to just want to get it all over with, and the actors (except Hamill) are just pay checking it

It's too juvenile and toy-oriented

Han and Leia are given nothing meaningful to do

Fett dies embarrassingly

The ground battle on Endor is way too small and lacking in epic moments that the big finale should have

But it's not a bad movie per se, it's just bad compared with SW and Empire. Of course it's Casablanca compared with the prequels.