The book is (naturally) much better. There is no main character rather it is an account pieced together by an author after the Zombie War. So there is no Brad Pitt like character. It is a compilation of stories from soldiers, politicians, doctors, and civilians from the start of the outbreak, failed tactics of fighting zombies, changing tactics and eliminating the zombie hordes, to clean up and slow progress back for those left. Real cool stuff.
Yes I'd heard that, aside from the premise being about zombies, it's very realistic. So not the typical good guy, bad monster, good guy wins in the end. More how it would be if it really were real, many would fail.
Pitt was what I disliked the most about the film. I run hot and cold with him, he can be brilliant in a film (Fight Club or Twelve Monkeys) but other times, like in this film, he's so wooden he actually comes across boring.