This book basically tries to explain what Nibbana (sanskrit: Nirvana) is in Theravada Buddhist terms. Some people think that Nibbana is some sort of heavenly place, some think it's annihilation, some think that it's a "state", but none of these are correct. The concept of Nibbana is quite alien to western thought and Thanissaro explores its elusive nature using the fire similes used by the Buddha himself.
Thanissaro Bhikkhu (Geoffrey DeGraff) has a degree in western philosophy and not only covers the core meditative practices of Theravada Buddhism, but does so in a manner which elegantly bridges this eastern philosophy and practice with western philosophical tradition.
This book is "intermediate" in terms of difficulty. If you are not already familiar with Theravada Buddhism I recommend reading "What the Buddha Taught" by Rahula Walpola prior to reading Wings to Awakening. There is also a lot of good material at http://www.accesstoinsight.org/
In this book, the author openly advocates for pedophilia and incest. Part of this is the economic and sexual liberation of children, the idea being that they should be treated like adults.
Her vision of the future is disturbingly close to Aldous Huxley's Brave New World, though she spends a number of pages trying to differentiate it.
Basically this book is ridiculous and I don't understand how anyone can take any of it seriously. I only started reading it because it's in the bibliography of the book "Cognitive-behavioral treatment of borderline personality disorder" by Marsha Linehan. For those who don't know, Ms. Linehan is the person who invented Dialectical Behavioral Therapy, a very popular form of cognitive-behavioral therapy at the UMHS mental health department and many other places.
This is an excellent sci-fi book about the mind, life in digital form, and the ethics of staying in touch with reality. People interested in computers, cognitive science, and alternate ideas on what constitutes life will find this book interesting.
This book makes more reference to esoteric scientific concepts than previous Greg Egan books that I have read, in fact my cursory understanding of quantum physics was only enough to barely understand what he was taking about regarding that subject, but the book is still readable anyway as the more esoteric explanations are described in more analogous terms as well.
If you are sick of the usual Star Trek nonsense where the only thing that makes an alien is a different bump on their forehead, then this is a good book to read. Greg Egan is constantly pushing the limits of what constitutes life and what forms life can take.
I didn't like this book as much as Greg Egan's Diaspora and Permutation City though. I'd recommend reading those books before this one.