I wasn't all that impressed. The writing wasn't much better than a high school lit course would provide. Sure, it had lots of action but none of it was very well developed. I felt the soldiers were not military enough, esp. with a 3 star general just deciding to go AWOL with a haphazard little band of refugees.
I did like the difference in the zombie make up. There were basically 2 kinds of zombies, sprinters and shufflers. The sprinters are still alive but have been infected with a virus that acts a lot like rabies. If these sprinters are killed then they reanimate to a slower version of a zombie that also decays.
There is not much detail on the zombie itself (how long they survive, decay properties, etc.) and I feel this is a weakness in the story.