Most episodes of the series were not about those characters. That's the nature of an episodic series.
Star Trek the series was primarily plot driven. The movies were also plot driven, but a couple were character driven. However, in the classic Trek movies, there was character growth. Also, TV standards of the period required your hero to be the same person at the end of 51 minutes as he was at the beginning. Kept things easy for the syndication boys.
As for TFF, I always enjoyed it. I like all the movies, honestly, so they all get a pass in some way.
Pros: For a guy with a reputation for running roughshod over the “Gang of Four,” Shatner made sure each of them had something to do. Either interesting or humorous, but still more than Sulu and Uhura had in TWOK or TSFS.
Good, well shot and cut action sequences.
A sense of SCOPE. Not “on location in San Francisco” kind of cheap scope, but the “let’s build elaborate sets and shoot out in the desert” kind. Think about what this film had to pay for: a new bridge, a hangar deck, an observation room, Paradise City, two full size shuttlecraft, not to mention mostly new, straight from New Jersey special effects. Even when some of them failed, others were amazing. Plus, they had a guy climbing a real mountain (this is also a con).
Heart. You really felt the love between the Big Three.
Assault phasers and combat gear!
Of course, Jerry Freaking Goldsmith.
Amazing Klingon make-up.
Laurence Luckinbill. He makes you think this is a great film.
Khans:
Kirk free climbing a mountain. I would have bought the sequence if he used ropes. I mean, regular mountain climbing is plenty dangerous and there are lots of ways to fall screaming to your death. Chubby Shatner doing that would have been tough to accept, but still a lot more plausible than free climbing.
The fall: Kirk’s “whoooooooa!” and the godawful blue screen work (WIND anyone?) just ruiin any sense of danger. As soon as that scene was over, all of the atmosphere created by the pre-credits was ruined. It was gonna be THAT kind of movie.
Too much humor. I don’t mind character humor, but slapstick and pratfalls are just too much. They could have had humor without Scotty’s head bump, and Kirk’s “you made that up” stuff.
Shatner: really great at framing shots and planning sequences. Really terrible at self-direction. He was more over the top than ever.
The story: a dead end from the beginning. And to this day, Shatner believes actually meeting Satan, rather than an alien pretender, was a better idea. Why does being named director mean he has to create the story? Couldn’t someone else come up with something less horrible and have him direct it? Still, the film could have been saved with some rewrites and the excision of some of the humor.
The effects: ugh, when they’re bad, they stink on ice.
Anyway, I mostly enjoy it still, but I wish someone was tougher on Shatner regarding the story. There’s a great film in there, but not as is.