I enjoyed it. Some of the other reviews were negative, but I think that they may have expected a more scientific book (also, reviews of the kindle edition, or reviews published in newspapers and magazines, are generally positive). This book is written for a general audience, and the subtitle, "The Search For..." should be taken to heart. It describes the author's experiences and the people he met in his "search." While I didn't really perceive a strong focus holding the book together, the book introduced me to a bunch of interesting people, past and present, who know many languages. One particularly neat comparison was between some guy in northern California, who studied mostly by himself (through audio recordings and texts) and some people in India, who "picked up" several languages as they needed them due to the requirements of every day life in that part of the world. Different approaches towards similar results.
Overall, it's generally interesting and an accessible introduction to the world of people who know many languages.