First off, it's not a good movie. I would never make that claim.
But this film gets unfairly lumped along with genuine cinematic travesties like Battlefield Earth and Batman & Robin. I've seen dozens of big-budget sci-fi films worse than The Final Frontier in the last twenty years...including Star Trek: Insurrection. There are a few moments that work quite well - which I'll discuss in a minute - but the main story is weak, obvious, and downright goofy. And Shatner's inexperience as a filmmaker - not to mention various other setbacks and budget constraints - does nothing to help the translation of one of the weaker Trek scripts to the big screen.
Did Paramount make a mistake giving Shatner a chance to conceive Star Trek V's story and direct it? Probably. No matter the quality of the film, having Shatner as a credited writer and director painted a giant bullseye on Star Trek V. It's a punchline that practically writes itself. The film was never going to get a fair shake - and the end product is, to me, quintessential Shatner: big, over the top, dopey, yet strangely enjoyable. It's a guilty pleasure. I won't lie: along with II and VI, this is one of my sick movies.
The story is built on an interesting but flawed premise: Kirk and company go on a quest to meet God. Of course, any Star Trek fan above the age of ten only needs read more than that one sentence plot description to know that they'll never actually find God, nor would the filmmakers dare to prove or disprove His existence. The film ends with a trite - and obvious - "maybe God is within us" message: inoffensive to both doubters and believers. I don't know exactly what Shatner's original intentions were - but The Final Frontier has nothing meaningful to say about religion or humanity's need for a God.
The film doesn't even dare to have an actual villain. Sybok, a Vulcan mad prophet of a sort, is neither formidable or credible as an antagonist, since Sybok's powers and his vision from "God" are never properly explained. There's nothing wrong with a sense of mystery - but there's a difference between leaving things open to debate and not knowing what the hell is going on in your script. Sybok's gifts (not to mention all that "Great Barrier" bullshit) fall squarely into the latter department.
And it doesn't help that the filmmakers went the Days of our Enterprise route and made Sybok the half-brother of Spock. This makes Sybok someone that Spock has to care about, instead of wanting to care about. The idea of a passionate Vulcan - and a young Spock being attracted to his beliefs, his passion - could've made for one heck of a story. A quick rewrite defining Sybok's powers and making him an old friend of Spock's could have saved the last hour of this film from plodding melodrama and bland, inoffensive philosophizing.
And Shatner's ego is on display throughout the picture. This is Kirk's story, with Spock and McCoy the co-stars and the supporting cast that and only that. Kirk is the only one immune to Sybok's powers, and even has the balls to stand up to "God." A good chunk of the film's needless jokes are at the expense of the supporting cast.
OK...I meant to defend this film, but I've spent the last few hundred words giving The Final Frontier the finger. So what does the film do right? Why would I even want to defend it in the first place? The answer is simple: no other Trek film dedicates as much time to the relationship between Kirk, Spock, and McCoy, or nails the affection these characters have for each other and the affection that audiences have for them. I have always said this film works when the trio share a scene together - especially when it's just the three of them - even if the main story sucks. I stand by that.
The campfire scene in the first act and the reveal of "their pain" near the end of the second are the film's two most successful scenes. This is pure Trek - and if you don't agree with me, go back and watch the original series, which was often as cheesy, melodramatic, and silly as this film. Whether Shatner the director rises to the occasion or these scenes were strong enough on the page to be relatively foolproof is open to debate, but these scenes do work. Few other moments in the history of the Original Series capture the loneliness of these characters, or the regard these men have for each other...and, most importantly, how much they hate to admit it. True, this beat would have worked better if Shatner had regarded the entire cast as family, instead of just DeForest Kelley and Leonard Nimoy, but it's the one thing that makes The Final Frontier work for me, the only reason I own it on DVD, and the only reason I still watch it every few years.