I recently finished Darklost by Mick Farren.
This is book two of a series of vampire novels, the Victor Renquist Quartet. I got it because it mentioned Cthulhu on the binding and was free. I haven't read the first book in the series, but I didn't experience any trouble following the plot.
Victor Renquist is a thousand-year-old vampire (of course) who has recently moved to the LA area with his colony of other vampires, after the events of the first book made their previous home untenable. While there, he discovers a plot by a religious cult (almost certainly based on Scientology) to summon Cthulhu into the world, while also dealing with a pair of humans who want to become vampires (including an expy for Marlon Brando).
It's not really Cthulhu Mythos, or even Lovecraftian, in any particular sense. It's not really even horror in any particular sense, except that it exploits horror tropes. It's an urban fantasy thriller story, with Renquist running around with a sword chopping people's heads off. That said, it's pretty well written, and pretty good if you're into that sort of thing.
My one really big problem with the book - aside from one or two really handwavy moments - is that there are no really sympathetic characters. The vampires are unapologetic serial killers. They don't even have the Anne Rice "only kills bad guys" bit; they are serial murderers. The humans are a mix of insane cultists, vapid Hollywood schemers, con men, and vampire wannabes. Now, I've written Evil Protagonist stories myself. But, one, there were literally no non-evil characters, and two, the book didn't really bother to address the fact that the protagonists were all horrible people. It acknowledged it, but didn't address it, and I was left feeling like I'd read a book romanticizing serial killers.
That said, that's very much a matter of personal taste. So if you like vampire fiction with an action focus, you'll probably enjoy this. But, it's not my personal cup of coffee. 3/5 stars.