One complaint about TUC is the sudden, out of nowhere racism of the senior crew of the Enterprise, especially Kirk. It's an especially odd contrast to the end of TFF, where the Klingons and the TOS crew are drinking together on the ENT-A.
I don't think the sudden racism was necessary for the film to make its point. Kirk and crew distrusted the Klingons for political and military reasons, not reasons of race prejudice. If the allegory is the Cold War, anti-Communists weren't usually racist against "Russians" as a group, they were opposed to the Soviet system because it was seen as totalitarian and expansionist.
They should have played up the "distrust of the long time enemy" angle, and dropped the "Kirk is suddenly Archie Bunker" stuff. It's pretty jarring since it seems very out of character. Kirk has one previous reference to "Klingon bastards" and that's right after his son has been killed, and there's no other indications of racial dislike of Klingons until we get to TUC.