I love this book. 
 Jostein Gaarder's novel is a thinly veiled attempt to teach the basic history of western thought and philosophy. He succeeds doubly because the work he produced is both didactic and interesting. The plot of the book, i.e., Sophie's story, doesn't matter very much. They're just a vehicle - a transition, if you will, between the chapters discussing different philosophical movements throughout the western hemishpere. There is a bit of discussion of how the schools of thought differ from each other thrown in also. From Aristotle, Socrates, to Descartes, the Epicureans....it's all in there. 
 Of course, Mr. Gaarder is not able to fully explore and unpack each philosophy mentioned in the book, but he does an excellent job of laying down their basic principles and giving some context as to how these tenets arose. What he did especially well was to situate these movements in their history - so that one could follow these great thinkers/movements and understand how/why they arrived at various philosophies. And from time to time, historical people and facts would pop up to make said context and even 'realer' - I do even believe there was a mention of Paul of Tarsus in there somewhere! (view spoiler)[ It had me so shocked I reached immediately for my Bible and lo and behold - Paul was quoting the Epicureans! (hide spoiler)] 
 Totally recommended for lay students of philosophy. Heck, for college students taking Philosophy 101, I'd venture to say this book will help a great deal and probably be more interesting than your assigned reading. Also recommended for anyone really. In fact, for such a pedantic book, the narration is simple, clear, informative, factual, and interesting, a fact that cannot be overstated. 
 This book got me thinking about the fundamental and unquestioned theories that directed my life and our societies in general- at a time when I wasn't interested in Philosophy or theories. I was looking for a good time when I picked it up, and I got that and so much more. . 
 A very remarkable book, whose whole is so much more than the sum of its parts. Surprising and outstanding. Made of win.