I really struggled with how to rate this, because I was so ambivalent while reading it. There were sections I loved and sections that I really had to work to get through. The plot is so unique and such an interesting concept: an apocalyptic book in which the epidemic is language itself. Children's speech becomes toxic to adults, and problem spreads as other forms of communication (writing, sign language) become harmful as well.
This book has a lot to say about interpersonal relationships, because really, without a way to communicate aren't we really all alone? It's really interesting to see how people adapt and continue their lives while on the brink of death, without so much as making eye contact with their loved ones. I especially liked the portrayal of Esther, the teenage daughter, and I think Marcus's goal with this book may have been to explore that alienation between the generations. Right, it hurts when your kids get too cool for you and diss all your interests and stay out all night, but what if being close to them is literally killing you? Sometimes I felt like I was being hit over the head with metaphor, and at others I thought it seemed too obvious and maybe I just didn't get it.
A few more issues:
I found the concept of the Forest Jews intriguing, but I wish we were given more information about their history and culture. The different, future form of Judaism just didn't really make sense to me in the context of the novel and I don't understand what point Marcus was trying to make. First it seemed the Jews were being blamed and persecuted in a Neo-Holocaust type scenario, then it seemed like the Jews were the answer to stopping the virus, then it all just sort of fizzled out. I don't get it.
Also, the main character, Sam, seems to be having an identity crisis throughout most of the book. He starts out being like an everyman father character but then becomes, in short order, an expert chemist, biologist, linguist, and spelunker. Can you say Marty Stu?
I did really like elements of this, though! The prose is absolutely beautiful. Marcus creates some wonderfully creepy imagery, and has a real gift for showing human nature -- the good, the bad, and the ugly -- especially in such an alien environment. For example, this book contains probably the least sexy sex scenes ever written, but they're extremely powerful. I have a feeling this might be one of those books that lodges itself in my brain and I like more in retrospect, purely for the memorability factor.