This book has pretty much nothing to do with the movie starring Brad Pitt, other than the title and a few of the events, but other than that the two stories are completely and totally different.
The book is an oral history written down. The journalist decides to interview a lot of people who have survived World War Z and get their stories down. He breaks it up into a chronological history. How it starts and who knows about it; how it spreads...the Great Panic; etc. He gets stories from various people in different countries. So we get a picture of how the whole world handled this war.
A few of my favorite stories:
The Italian military buried beneath in the catacombs. That was scary. The few survivors trying to make it up north to Canada where it's so cold that the zombies freeze. The story about a woman who is guided to safety through zombie jungle by a strange voice on the radio. The under water zombie divers. How the dogs were trained and contributed to the war effort. How Russia becomes a Holy Empire again...
The only thing I'd complain about is some of the stories were a bit dry but that's to be expected. I think it makes the stories more believable as a whole.