I don't know exactly why, but I have a soft spot for trashy horror novels. You know the kind I'm talking about--quick reads that can usually be summed up as "monsters show up and whittle down the cast one by one", cover art that's usually a picture of said monsters, and titles that are either thuddingly blunt, like "Werewolf Moon", or so lyrical they're almost purple, like "Die Softly, My Darling", or lazy puns, like...well, like "Dead Sea".
Basically, what I'm saying is that this isn't really a good horror novel. It commits a lot of Brian Keene's usual sins; he comes up with a really interesting idea for a novel about apocalyptic societal collapse, something that nobody else in the genre is really doing, and then he has a first-person narrator skim through that idea in a five-page infodump at the beginning of the book so that he can get to a small cast of people running around with guns and shooting monsters for two hundred pages. Then, once the cast is sufficiently whittled down, the narrator gives a bleak coda. Admittedly, after "The Rising" and "The Conqueror Worms", I kind of knew what I was getting into, but it doesn't make it any less frustrating.
It doesn't help that this one is a little less inspired. "The Rising", for all that it didn't really make much use of the central concept of sentient zombies, at least had that as a compelling and unique hook. And "The Conqueror Worms" was bizarre, but it was so bizarre that it was downright fascinating. This is just, "Oh, hey, zombies. And zombie animals too, that's kind of different, right?" (It is different, but it's different on a level of, "You realize everyone in this book should be dead before page one, right?" A zombification virus that crosses species would result in an almost inconceivable holocaust, and I don't think Keene really got an idea of the scope of the devastation.)
But yes, "Dead Sea" is pretty much just zombies of all species. Survivors escape to the ocean, there's two hundred or so pages of running around and shooting things, and once the cast is whittled down sufficiently, the narrator gives a bleak coda. I think the big problem is that the end is simply too obvious; given that civilization has already collapsed, food and drink is impossible to obtain due to the fact that everything is already dead and still moving, and the virus keeps jumping species pretty much willy-nilly over the course of the novel, it's hard to even imagine that this won't have a bleak ending. It's hard to generate tension when all the characters are basically just "pre-dead"--you just can't get attached to them enough to care. (It doesn't help that they don't really sound like real people. There's a scene about two thirds of the way through where everyone just starts chatting about Jungian archetypes that is absolutely immersion-shattering in its sheer unbelievability.)
That said, Keene has a slick and propulsive narrative style that makes the book a quick read and an easy page-turner. You don't really get invested in the consequences of events, but the book moves smoothly from one event to the next without any real languors (apart, perhaps, from the aforementioned Jungian archetype conversation). There's also a vividly creepy human monster in the form of a priest who believes zombification to be a miracle and enacts his own perverse version of the transubstantiation myth, who really should have been given a more prominent role. Those sequences are probably the best bit.
So that's "Dead Sea". As long as you understand what you're getting into, it's a decent read. But like all of the guys who are listed as "the next Stephen King" on the back covers of their books, Keene is no Stephen King.