This is a sequel to Darwin's Radio, and it is probably better if you read that one first, but probably not necessary. Understanding what's going on requires a pretty good understanding of some relatively high powered biology. If you're current on Bear's writing, the earlier books (Darwin's Radio and Vitals) probably taught you want to need to know, but if you don't feel conversant with ideas like what a retrovirus is, read the section at the back called "A Short Biological Primer" (it's only a couple of pages) before reading the novel, and refer to the glossary after the primer when you hit a scientific term you're not sure of.
This is a book that presents interesting ideas to think about in science and also in social speculation. It is pretty successful in presenting those ideas. It is unfortunately less successful as a narrative. The story jumps frequently from one viewpoint character to another, with what seemed to me an excessive use of cliffhangers -- just as something exciting was happening on one story line we often jump to another. A lot of authors frequently juggle multiple viewpoints in a way that seems less disruptive. However, the major problem I have with the way the book is written is that it is divided into 3 parts. One part ends just as things are getting really exciting for the overall plot, and the next part picks up 3 years later leaving the reader to piece together what happened at the end of the preceding part. I have no doubt that Bear did this on purpose for what he saw as good artistic reasons, but I found it extremely frustrating and disruptive to the reading experience.
What's really interesting about this book is the theme of how humans as we know them today would react to a significant jump in evolution happening around them. There is tremendous fear and hatred directed toward the SHEVA children. I believe we are meant to recognize that people are irrationally overreacting to the medical danger because the children are different, rather than coming to fear the children because of the medical danger. He predicts, it appears, that "normal" human beings would hate and fear evolutionary advance in general. And I think that he's right, which I find sad in itself, and depressing in that it points out how much I don't fit in with ordinary humans. I find the SHEVA children fascinating in the book, and while it's hard to really know, I like to think that I would be interested and supportive of such a change in the real world.
Tough to put a rating on this. There are interesting and provocative ideas I enjoyed reading about, that I'd like more people to be exposed to (and that I hope others would find interesting), but I had a lot of trouble with the actual story and the way it was chopped up. If I give the ideas a 9 and the writing a 3, I can average that to a 6, and let you decide how to weight those. The individual scenes are quite well written, but they're very badly strung together.