I actually read a particularly bad Star Trek novel recently; I shan't shame the authors by naming it or them directly, but it was definitely one of those stories where you could replace the so-called "main" characters with an inanimate object - a couple of pineapples, say - and not change the plot in the slightest.
It featured a love interest for both Kirk and Spock (who, despite never having met her before, having no way to expect her presence beforehand, and her work being completely classified, were able to identify her by name the moment they met and fell in love with her) who was a "Free Agent of the Federation" - which meant she was basically a higher rank than Admirals, even, without having any of those pesky regulations or exhausting paperwork to deal with - and more advanced in the Vulcan philosophical disciplines than Spock was. Without, you know, displaying the emotional dampening, reserve, and discipline that is the entire point of said disciplines. For some reason, I kept misreading her name as "Mary."
Spock was also written poorly. There's some nods to the fact that he's supposed to be logical and unemotional, but I could hardly tell behind all of the scowling, brooding, anger, and melodramatic displays. And then none of the other bridge crew apart from Scott and McCoy get any role in the story. Even Kirk and Spock are basically there to be her motivation, rather than to have any active role in the story; it's "Mary" who is at the centre of the conflict and ultimately resolves it.
I was also rather annoyed to find that none of the characters made any real arguments about the central conflict, but instead followed the same route every time:
AMBASSADOR DEVIL: "It is better to surrender your individuality."
KIRK; "My gut says it's not."
AMBASSADOR DEVIL: "Yes, it is, and if you don't believe me, I'll force it on you anyway. I'm such a nice guy!"
KIRK: "Well, good thing you said you were nice, or I'd actually have to do something! Would you mind helping us out against the guy who wants the exact same thing as you?"
AMBASSADOR DEVIL: "Sure, but I'll steal your soul, and I won't give any really meaningful help."
KIRK: "Great, thanks!"
(No, his name's not Ambassador Devil, of course, but he's still directly called the Devil by just about every character he meets, as part of a heavy-handed metaphor about Job. Somebody needs to look up subtlety in the dictionary.)
There are a lot of good Star Trek novels - Uhura's Song, Dreadnought!, and Sanctuary are all treasured volumes in my library - but there's a lot of execrable ones as well, and that book is definitely one of the latter. On the positive side, it's not particularly memorable; if I hadn't finished it just the other day, I wouldn't still be annoyed with it enough to write about it when I spotted this thread today. There are cats out there that do far more interesting things with pineapples than it did - and the pineapple has less to feel ashamed of afterwards.