I am reading The Variant Effect by G. Wells Taylor which has been enjoyable. It isn't strictly speaking a zombie book, but there are enough similarities that it might be worth a shot (especially since it is free). There are a couple writing quirks that I don't care for, but nothing strong enough for me to stop reading it or make me want to avoid the sequels.
It is available free from Amazon, Smashwords, etc. Or from the author's website:
http://www.gwellstaylor.com/blog/