This has come in for criticism from fans of the book, but having read that first, I have to say, it's pretty close to unfilmable in its original format. The "oral history" approach, means it's told from literally dozens of different viewpoints, each giving a tiny snippet of the overall picture, which might work for a pseudo-documentary, but when you're spending $190 million on a film, you're probably going to stick to something with a more traditional dramatic structure. So: it's not the book. Get over it. What it is, however, is the first truly large-scale zombie film, with tens of thousands of the goddamn things, and that's where this works incredibly well. If you don't find yourself mouthing the word "Wow" during, say, the breach of Jerusalem, you're a more jaded and blasé hack than I. There is stuff here which you won't have seen in a movie before, I can guarantee it, and that's certainly a significant part of why you watch films: to experience the unexperienceable.
It's perhaps significant that Forster directed Bond flick Quantum of Solace, because Brad Pitt's investigator whizzes around the world like the epidemiological equivalent of 007, trying to find the source of the disease which turns humans into enraged monsters in less than 30 seconds. This takes his from Korea to Israel to...er, Wales, and you can't argue that the large cost is not up on the screen. However, as a zombie movie, it doesn't succeed in generating any significant real tension or sense of dread, largely because it's so busy galloping frantically from one large set-piece to another. This was apparently noticed, and addressed in a final act that I think was largely re-shot, with the hero creeping his way through an infected health research facility (I was amused to find new Doctor Who, Peter Capaldi, here playing a WHO doctor...), trying to find the samples that could hold the key to turning the tide. It's a lot closer to what you're expecting from the genre, though doesn't quite gel with the rest of the film. Overall, while certainly not the book, it contains enough memorable sequences that you don't feel short-changed, and brings the threat of the zombie apocalypse to life in an innovatively large-scale manner.