The obvious comparison of this book is with the novel Lolita. Both books are ambiguous as to what is going on. In my interpretation, both books are about the self-justifications of a delusional monster. At the time Lolita came out, there was a much lower level of awareness of child sexual abuse and it was possible for people to take Humbert Humbert's delusional self-justifications seriously, see for instance the review of Lolita in the Portable Dorothy Parker. This is also about the self-justifications of a monster.
Apparently, the author wrote the book as deliberately ambiguous as to what is meant to be going on. We can read it so Eva, the mother, is the only one who is aware that her son Kevin is a monster or we can read it where she is the monster who basically drives her child to kill. The main character, Eva, can be seen as merely a mother who failed to attach to her child, but her problems go much further than that. She clearly sees Kevin as a monstrous alien from the very start and bares some to all of the blame for what happens. The relationship is one of profound and very serious emotional abuse and our society is blinder to this sort of thing than the 1950's was to sexual abuse. Even if we suppose that Kevin was born a sociopath, this is no excuse for Eva's behaviour. She is not indifferent to her son, but treats him as an enemy from the moment he is born. She becomes obsessed with school shootings and links Kevin to the shooters long before Kevin shows an interest. I'm not really sure that Shriver understands what she wrote here, but she is channeling something. Some people see this as a feminist book. I think that it shares something in common with The Awakening in that the protagonist uses laudable feminism to justify child abuse. I think that is not an uncommon phenomenon in our society, by the way.
It is really a brilliant book in so many ways. Eva's self-delusions and character are masterfully done. Her paranoia sucks you in and you are often consumed by her ways of thinking. It has a slow build. Eva's character is really brilliant, her husband emerges as a real person. It is a meditation on evil primarily, on how it works and what it looks like. Eva is an evil person, who, like most evil people, does not know that she is evil. I think that this might be a case of the author not really understanding an aspect of the book. Tolkien always said that The Lord of the Rings had nothing to do with World War I or II, but it is really naive to read that book as having nothing to do with those wars. Eva is basically insane and evil, and psychologically tortures her son. Some see this as a work about guilt, but to me what is striking in Eva is the lack of guilt and responsibility and the fact that everything is construed against Kevin.
Kevin emerges as a real person at the end, and his ambiguous feelings towards his mother - his love and hatred towards her as the motivation of his acts - come out.
The other flaw is that while Nabakov was a master prose stylist, Shriver is not. Shriver's ideas and even her word choices are excellent, but the way she puts together a sentence, is not pleasing to me. I don't find it annoying as I occasionally do with some writers, it's fine, but I find it just the right side of clumsy. Having said that, I have known a person who was a worse version of Eva. It helped me to stop excusing that person.
It is not clear to me if Shriver is a very talented writer or if she was channeling the muses with this one and it will take further reading of her to know. It has problems with its prose style, but everything else about this book is fantastic. Recommended.