CAVEAT: I've known the author for several years, and he consulted me regarding some of the novel's military content. He even sent me the copy I read. Having said that, I wouldn't have reviewed the book if it sucked, and that's about all I figure I'd owe him. I think John would agree.
I've read a lot of zombie books, and I'll probably never stop reading them. THIS DARK EARTH does contain a few of zombie fiction's tried and true plot devices--mainly because acting as though the the zombie apocalypse WOULDN'T bring out the worst in humanity is the height of idiocy. It also contains several great characters--Lucy, Knock-out, Gus, Tessa, Broadsword and Wallis, to name a few. Every part of the book is heartfelt and possessed of a sensitivity I wouldn't have expected from John--and which, along with John's unique style of writing, sets the book apart from the rest of the zombie genre.
There's a slim chance I've read a zombie book as good as this one before--like I said, I read a LOT of zombie fiction. THE RISING is probably this good, if you really need a comparison. The Woodbury (Governor) story arc of Kirkman's WALKING DEAD (though that's really comparing apples and oranges). But nothing comes to mind as being better. If you're a horror fan, and even if you're growing tired of the living dead, pick this one up.