An old review from rec.arts.startrek of a miniseries that kicked off the crossover trend and still gets discussed fairly often...
"Emotions Crashed Across His Face"
Time for a quick review of the Invasion miniseries. The subject line is a quote from the stylistically challenged Diane Carey. She failed to report whether the crashing of emotions across one's face results in bruises, abrasions, or, for that matter, sound effects. Still, it doesn't sound pleasant.
Diane Carey's TOS novel is, as might be expected, a paean to the embodiment of all that is good in mankind, James T. Kirk. I'm not quite as fond of Kirk as she is, so the scenes in which characters tell each other how superior Kirk is because he befriends The Other (as a general concept) while others fear and flee it didn't do much for me. And her usual military fetish results in a long, drawn-out battle sequence beginning the book. It has essentially no relevance to the Invasion storyline; instead, it's a minisequel to the TOS episode Friday's Child, inserted to show what a fighting he-man hero Kirk is. Boring.
Fortunately, the novel picks up the pace when the focus is on the Furies. Carey, unlike the other writers in the series, describes the Furies as a civilization in their own right, and has at least one sympathetic character among them. They aren't just cardboard cutout bad guys. Of course, the key gimmick is ludicrous. All races in the Alpha Quadrant have a dramatic, instinctive sense of revulsion when they see the Furies because the Furies invaded our worlds five thousand years ago, when we were primitive, and we modelled our evil deities on them. This is patently ridiculous for at least three reasons: it assumes the existence of some kind of genetic race memory (a la Quatermass and the Pit); it assumes that all cultures in the Alpha Quadrant were at the same point of early civilization 5000 years ago; it assumes that our usual visual representation of the devil as a goat-man with horns is 5000 years old instead of a few hundred years old. The concept of Satan in the Judeo-Christian world is a hell of a lot less than 5000 years old, and it's changed a lot in that time, too. It doesn't help that the basic idea is a bit too reminiscent of the TOS episode Who Mourns for Adonais and the TAS episode How Sharper Than a Serpent's Tooth, in which we learn that some gods of legend were actually visitors from space. IIRC, the TAS episode The Magicks of Megas-Tu covers similar ground, with a devilish character named Lucien.
So the concept is dumb. Carey, though, keeps the action moving well enough to gloss over the unlikeliness of the whole thing, and only occasionally reminded me of how much I usually hate her books.
On the other hand, I usually enjoy the Rusch & Smith books; they aren't the best, but they're always at least competent, and often quite good. But their TNG novel for Invasion is a bit of a dud. Suddenly the Furies are purely evil, one-dimensional bad guys, and not terribly interesting. So they pour on the action and set the stage for the Voyager novel. Readable, yes, but when Diane friggin' Carey makes me sit up and pay attention, I expect to be blown away by Rusch and Smith. It didn't happen, though the end of the book is reasonably intense.
I've enjoyed most of LA Graf's stuff, but their DS9 novel was so much the highlight of the series that it surprised the hell out of me. (Of course, I am a DS9 fan, but even so...) Among the remarkable things in this book: the Furies don't appear, but their ancient adversaries do, and they're a lot more intriguing than a bunch of bad-tempered demons; there's a twisty, complex time travel element that starts the novel with a hell of a mystery and has a good payoff later; attention is paid to the unique political and character dynamics of DS9; the dialogue is often sharply crafted, the characters well drawn. I like it. Anyone who doesn't give a flying wallenda about the Invasion series as a whole should still give this one a look. It's closer to being a standalone novel than the other three.
Dafydd ab Hugh wrote one of the most intense DS9 novels yet, Fallen Heroes. His next novel was a bit of a letdown. His Voyager novel is somewhere in between. There's intensity to spare, and audacity on a cosmic scale (tossing the Furies' Delta Quadrant adopted homeworld to one of the Magellanic Clouds is almost over the top), but it suffers in comparison to the DS9 book. Time's Enemy had a hell of a lot more going on than just some worry about what the Furies were up to. Final Fury is a more tightly focussed book, which may make it better for some readers, but the characterization and dialogue weren't as strong as LA Graf's.
As for Invasion as a whole...
Worth reading? Sure. It's not literature, but it's entertaining, despite its silly premise. There wasn't really any need to tie the ancient representations of evil stuff in; any large invading force would have done equally well. The Soldiers of Fear is the only book that would need extensive revisions to get rid of that element, and it was the weakest entry in the series anyway.
In closing, from best to worst: Time's Enemy (DS9), The Final Fury (Voyager), First Strike (TOS), The Soldiers of Fear (TNG).
If someone had worked with Ms. Carey to improve her idiosyncratic prose style and dampen her ardor for Kirk, First Strike could well have taken second place. But, apparently, the writer of such unforgettable gems as "Emotions crashed across his face" and "Worf was plied with shame" is too popular with the average Trek consumer to worry about the quality of her prose. As seems to have happened on a much larger scale with Stephen King and Anne Rice, Carey can write badly and fans will buy it anyway, so why bother to edit.
But I digress. Overall, a worthy effort.