It's no spoiler to say this is a zombie book, because you find out in the very first chapter. The hints that give away the children's nature are creepy, and that first chapter was fun to read because it's so uniquely told--from the zombie child's POV, when even she doesn't know what she is.
One thing I really like about this book is the pacing. I rarely got a moment's rest, a moment to feel comfortable with the "new normal" of the situation. This holds true for most of it, until the middle, when it devolves into typical zombie fare for a time. That's really one of my few complaints: the characters spend a large portion of the middle chapters doing the usual fight-or-flee from zombies, holing up at night, scavenging for food, dealing with the creepy horror factor, and so on.
I understand why the author (who I was surprised to find out is a dude...) had to switch viewpoints throughout the middle of the book, but I was kind of hoping that more scenes would take place from Melanie's POV. At times they were quite few and far between. There were also a few times where I wasn't sure for several paragraphs whose POV we were in.
As always, when a work is so close to perfect, it makes the few faults it has stand out, but by no means should you take my criticisms above as a reason not to read the book. The middle of the story gave birth to something far more fascinating as the characters and I pieced together the puzzle of the fungus and its true nature.
And the ending... While it is a bit abrupt, I loved it and the implications of it. I'm glad it doesn't devolve into sappy romance and that there truly is no happily ever after. I'm also glad that both Parks and Helen get a chance to redeem themselves before the end. Like Mad Max: Fury Road, the location/goal that the characters thought they were trying to reach (Beacon, in this case), isn't where they end up.
There was just one thing that I was hoping to find out, and that is whether the children age like normal people or if they will become a race of immortals. Unfortunately this was never made clear to me. But the tragic ending is befitting of the tragedy of the opening, and it works so, so well.