On the contrary, I think STVI is overrated. Why are the characters treated so badly? Kirk's suddenly a racist, McCoy is incompetent (no idea about Klingon anatomy?), Uhura can't speak Klingon (the communications officer doesn't know the language of the Federation's main rival?) and Spock mind rapes a screaming Valaris on the bridge while everyone just sits and watches.
And the less said about that Shakespeare-obsessed Chang, the better.
It could have been so much better with some rewrites.
Those issues always irk me too, but it is still one of my favorites. Sometimes your opinions about a particular work of medium are less about the piece itself than where your head was when you came to it. Which to my mind explains things like N'Sync and anything with Adam Sandler.