This is a must read. Character development is excellent, envisioned world has some fresh ideas. Dialog is pretty good (for a zombie book). Overall just well executed.
I have read a LOT of semi pro zombie series that have thousands of very high ratings that are incredibly marginal books. This is not one of those.
The character's emotions and actions are believable. No crazy coincidences, stupid luck etc to get people in or out of trouble.
An example of a series with a large popular folloing is zombie fallout. I gave up reading zombie fallout to book 4. That series was absolutely horrible (unless you like juvenile comedy fart jokes which many do - like deadpool).
This series is a serious book, well written, with characters that are consistent and have a good backstory. There is even some moderately sophisticated philosophy going on as well.
I would put it in the same league as books like the dust/wool series, day by day armageddon, forest of teeth and hands and the remaining as far as being engaging and enjoyable to read.