I watched World War Z tonight and really enjoyed it. (4/5 stars--very tiny spoilers in this post). I love how the amazing book and movie actually go together. The book was impossible to film, and this story adds a really interesting thread to the overall event.
I listened to World War Z on audio book (the 14 hour version) three times (I've never actually read it), and I think the movie is a great introduction to the novel, as the movie happens earlier than the book, which is a retrospective look at the zombie war with Max Brooks (the author) traveling around the world interviewing people about what happened.
Anyway, the movie was scary, intense, emotional, action-packed, well-acted (Brad Pitt was awesome), and paid great tribute to the book. The book and movie are very different entities and I recommend that you watch the movie, and then get the unabridged audio book, which is voiced by A-List actors. If you're a zombie fan, I think it's better to see the movie before reading the book. I think this is a rare case where the book and movie go great together, rather than clashing so much. The book is better, but the movie was excellent.
Here's a great article with links to what led up to the decision to re-shoot the ending of the movie. I found it fascinating. I like the version they went with, but I'm looking forward to seeing the deleted scenes. Read the article here.
I've read all (most?) of the articles linked from this one, above. I'm so glad they changed the ending, as I think this one worked really well. The scenes in Russia (that they filmed in Budapest), will be interesting to see someday. It appears to me they made some big mistakes by not having a strong plan or strong leadership. Starting a movie this big without knowing the ending was a bad idea. At least it worked out in the end, though the cost was high.