It's a perfectly fine zombie movie, but it only takes small elements from the excellent book. The book needs to be a TV series, made in a documentary style. I just pretend the movie is unrelated; it's enjoyable as just a standard action movie with zombies in it.
It would have been so easy to do a straight up adaptation of the battle of Yonkers, narrated by Mark Hamill, his two following parts, and a few of the smaller stories here and there to flesh things out, too...