It's not quite as straight forward as that. The book is essentially a compilation of "in universe" interviews with people from all over the world and in all walks of life who lived through the whole thing, so you "see" the whole thing on a much grander scale than the average Zombie Survival story, while at the same time retaining the street level perspective. What it's really about, to me at least, is how people - from individuals, mobs, groups, nations all the way up to the species in general - deals with and adapts to (or not, in some cases) extreme stress and upheaval. In fact, for the most part the zombies themselves are barely in it. I can only think of a few chapters that deals with the Z-heads directly and most of them are the recollections of military types. The one involving a pilot, crashing in the middle of an infested zone springs to mind.
Stories and especially movies that drop a bunch of characters right in the middle of a zombie infestation are all very well and good, but it's been done, many many times (and done well too) rather than just beat the proverbial undead horse, this book dose something different and I think rather unique and compelling.
Oh and any zombie story that has Nelson Mandela in it has GOT to be worth a read.