I do love it when anyone who has anything negative to say about something is labeled 'a hater'.
My opinion of the film comes from seeing aged it 13 and hasn't really changed since so I can't really put it down to being older (though some would argue I have been 40 years old all my life and my body has just caught up with the rest of me, which will probably start regressing now to the point where burp jokes and teddy bears smacking themselves in the head will begin to look like great cinema).
People are different.
There are people on here who love TPM because they are young enough to be nostalgic for it.
The same goes with ROTJ.
But if you brake the film down, look at the art design, the writing the acting, the attention to detail, even the score, ROTJ is the weakest film of the OT and set the scene for almost everything wrong with the PT.
Some people would argue that on first viewing those things aren't noticed and that thanks to the VCR and the home viewing formats that followed, these films are placed under much more scrutiny than they were designed for (an opinion I wouldn't entirely distance myself from).
But I noticed the drop in quality back in 1983 and as you have read I was not alone there.
I grew up watching Doctor Who and Sapphire and Steel so normally I would be forgiving of things that might not look so hot but still had a strong story of compelling performances but this is Star Wars, the film series that gave us :
In ANH and ESB almost everyone gives a good performance and the films still look amazing for their time in the same way that Metropolis and Forbidden Planet look amazing for their time.
ROTJ looks and feels tatty and unloved, like a nativity play using last year's costumes and Mark and Ian give the only two performances that really shine out of the fog, for everyone else it's the contractual obligation picture.