I read World War Z back in high school. I found it to be an interesting take on the zombie genre that attempted to explore the "real world" implications of a zombie outbreak and proceeding war. It was a book filled with sarcasm, themes of humanity, and allegories relating to the current state of society. When it was announced that the book would be adapted into a film starring Brad Pitt, it was fairly obvious that the filmmakers would rid the story of all the substance that made the book engaging and thought provoking.
The result is about what I assumed. While the first two/thirds of the film present a zombie outbreak on a massive scale with impressive set pieces, a tragically awful final act destroyed any possible enjoyment, at least for me. The film is ripe with cliches and poor scripting that leads to a movie that is visually appealing, but lacks any true structure as a narrative. Seriously, I can not stress enough how awful the final thirty or so minutes truly are. It reminds me of Huck Finn, it's almost like at the end the writers just gave up and said "eh screw it, this works." No Mr. Screenwriter, it really doesn't.