Calling any of the 'Star Trek' movies "unwatchable" is just hyperbole. None of the eleven films falls anywhere near that category, even compared to similarly budgeted major motion pictures. Some of these movies are better than others, that's just a given, but some of the claims made on this board are just totally ridiculous.
I actually agree with this sentiment. It's all a matter of preference, I suppose; if anyone
truly finds their least favorite Trek films "unwatchable", then fine... but I question how many really, truly AWFUL movies you've seen if you say that.
On TFF: it's a close call for my least favorite film between it and TMP, though I have to give the "nod" (or am I giving it a kick in the teeth?) to TFF. They are both bad for different reasons, but at least TMP - despite being stiff, slow, pastel, and utterly boring - managed to maintain a modicum of intelligence, and was shooting for high-concept sci-fi as its base plot driver, rather than a villain-based action piece (something I wish at least ONE of the other Trek films would have attempted...). Whereas TFF is just... stupid. And I don't think much of the concept; it's not just the execution that drags it down (though, don't get me wrong: the execution is abysmal).
Ah what the hell, I'm already posting, so following
Tiberius' lead, here are some more off the top of my head:
-Sybok is a terrible villain. He fluctuates between goofy and vaguely creepy throughout the entire movie. (I still love the suggestion by Phil Farrand of Nitpicker's Guide fame that the song "The Laughing Vulcan and his Dog", suggested by Marisa when Picard asks her if she can think of something for the group to sing in TNG's "Disaster", refers to Sybok and that freaky chap he meets at the very beginning of the movie).
-Nimbus III. What is the point of this place? We are told what it is, but never why it's on this backwater nothing planet, which strikes me as pretty much the worst place it could be. Also, Sybok needs a ship. To leave Nimbus III and search for God. Pop quiz: how, in all likelihood, did he GET to Nimbus III? Perhaps... on a
ship?
-Speaking of ships, why was the
Enterprise such a complete mess? NO new ship would be anywhere near THAT unfit for deployment, and yet still be deployed. And the admiral says he needs Kirk out there, if memory serves. Can't they just stick him on another ship for a bit if the Ent-A has THIS many crippling bugs to work out. But that's all moot anyway: the Ent-A
isn't even a brand-new ship at this point.
-Managing to outdo even the majority of the "lol Starfleet Security" moments from TOS and TNG (a feat) is the scene where Kirk and his team are defeated by those half-wit natives and their guns that shoot rocks.
-What DOES Sybok do to people? Is it actual brainwashing? If so, how DID Kirk resist? If not... that doesn't say much for the loyalty and willpower of Kirk's longtime friends and colleagues.
-Why are the special effects in this movie so god damned TERRIBLE?
-The fan dance.

-And finally, we have the (inexplicably green) photon torpedo that the
Enterprise fires at "God", which hits the ground and explodes with all the force of a handful of firecrackers.