The actual zombie infection I thought was very well done. It makes sense that the first responders would be among the first and hardest hit. The chaos throughout the city is also entirely believable.
I liked that McKinney referenced zombie movies. It made the setting grounded in the real world. I also really liked that there was a character who was a member of something like the Zombie Research Society
The fact that some people held onto old prejudices also helped ground the story in reality. Sure, in the face of imminent danger people might work together, but when there's breathing room I don't think it's at all surprising that some people would retreat into their old prejudices. Prejudice is familiar at a time when everything around them has changed. People might band together against a common threat but that doesn't mean they're all going to become best friends. Maybe there will be more understanding after, but maybe not.
The chaos and the horror felt very real to me. I enjoyed seeing how different people reacted to what was happening and it was great that not everyone survives.
The book is well done, probably 4 stars, right up until the end where it goes off the rails. The ending is a cop out. Our hero survives one night and then the military shows up and magically everything is not precisely normal, but much, much closer to it than it has any right to be.
I don't know why the military would be able to eliminate the threat any better than the police. American tools of war are not meant for individual head shots, they're meant to maim and explode. (For a better perspective on the modern military's problems against zombies I highly recommend Max Brooks' [b:Word War Z]). I simply don't buy that in less than a day the military could mostly contain the threat. Not happening.
I understand that the book had to end at some point and apparently it's not part of a series. But the ending simply doesn't make sense. Zombie outbreaks do not make for quick happy endings.