Star Trek VI treats the characters horribly.
-Kirk is suddenly turned into a racist Klingon-hater, totally at odds with the guy seen in TOS and as recently as STV. It's out of character. Remember hpw he treated Kruge and Maltz, so shortly after David's death? He offered his hand to the guy who ordered his son's death. He drank with Klingons in STV.
-Spock graphically mind rapes Valaris in the middle of the bridge, and everyone just watches. Nobody tries to stop him. I pretty much pretend this scene never happened, since the way they played it, Spock might as well have bent her over the helm and everyone else is an asshole for just sitting there and allowing it to happen. Out of character for Spock and everyone else.
-McCoy doesn't know Klingon anatomy. Klingons have been the Federation's #1 enemy for a century, yet the Enterprise doctor knows nothing? No way.
-Uhura doesn't speak Klingon? The communications officer of the Enterprise doesn't know the language of the Federation's #1 rival for the past century? Despite several dealings with them beforehand?
-Spock(again) talks with Jim about them both being old and useless. Spock is half-Vulcan, and wasn't close to middle-age at the time.
And FWIW, this film ignores "Yesterday's Enterprise", which had previously established that the event leading to peace with the Klingons was the heroic sacrifice of the Enterprise-C 20 years prior to The Next Generation. It prevented a war which the Federation would have lost. Compare with the Praxis explosion crippling the Empire, which had no choice but to sue for peace.
Instead of writing a story to fit the characters, they changed the characters to suit their story. A lot of Trek has done that over the years, but never so blatantly as in STVI.