What do you think of Peter Straub's "Koko"?

I was just wondering what this book is like. Like, this is a story about a zombie soldier who only wants to kill, and four war veterans are trying to stop him. At least that's what it seemed to me from the synopsis. And it has about 864 pages), which I think is a lot for such a plot. Those who have read, please write, did you like this book or not?

P.S. I know that this is part of a trilogy.