I usually read a series of books in order. Thankfully I went back and read the first book after I read this one. The first book almost sounded like it had been written by another person. It was choppy and structured like a maze. IMHO,it could have been boiled down to at most two chapters at the beginning of this book.
The book I have always compared apocalyptic books to is the classic, "Alas, Babylon". At the time it was written the United States was in the midst of the Cold War, with Russia rattling the nuclear option often. Published just a couple of years prior to the "Cuban Missile Crisis", it was every thinking persons worse nightmare. To put a slight perspective on the fear that was in place at the time, nine-ten months after the crisis, birthrates across America jumped by over 50%. In "target rich" locations, increases of nearly 200% were recorded.
While this book will not make such a measurable impact, it takes a fearsome possibility and brings it up close and personal. It puts fear of the unknown directly in our gaze, then shoves the known "Survivalist" mentality and preparations down our literary throat.
The techniques used by 'the unknown enemy' are now a case study in how to eliminate a large population while maintaining the greatest integrity of infrastructure possible. Get all the terrified lemmings in one spot and destroy them more efficiently and with less risk.
I still rate "Alas, Babylon" as the better of the two, but only by tenths of a percentage point.