Creator Backlash: While Gene Roddenberry didn't like any of the movies, he really didn't like this one. Several of the cast and crew also have low opinions of the movie.
Though most of the cast and crew have admitted they enjoyed working with Shatner because of the level of energy he brought as director.
Creator Killer: Despite having a long history as a successful TV producer and being one of the two men — the other being Nicholas Meyer — that saved the Trek franchise with the second movie, producer Harve Bennett's career was utterly ruined by the failure of this movie. Afterwards, he only managed to find work on two fairly obscure TV shows before disappearing from Hollywood.
William Shatner's career ultimately survived The Final Frontier, although obviously any hope he had of becoming a major director went up in smoke afterwards.
Executive Meddling: The original story idea from Shatner involved the Enterprise encountering Satan posing as God, and Kirk & Spock descending into Hell to rescue McCoy... which probably wouldn't have been suited to Star Trek anyway, really. The executives also demanded "More humor!" and slashed the film's budget, resulting in awful jokes and massive special effect failure throughout.