I can't really fault the book at all.
Robert Greene has established 48 laws of power, and they are all very interesting, powerful and fact based. Throughout the book I feel as if Robert knows completely what he's saying and he's done acres of research.
This book however, is to be taken very carefully. It doesn't seem as if he has written the book to any moral guidelines. If books can have age restrictions on a person buying them, I would definately give this one an 18. I could definately see someone young, greedy or just suggestable obsessing over the book and becoming a pretty immoral person. I believe it takes a certain level of maturity and moral understanding to be aquired in order to not abuse information in the book.
The 48 laws of power, generally focuses around methods you can use and themes you can engrain into your personality, in order to get things. Whilst the book is absolutely brilliant at delivering this, the fact is that if everyone applied all the laws to themselves (or even just a handful), the world would be almost at a standstill... as an example one of the rules is to "Get others to do work for you but always take the credit" - is this really a mode people should follow for the good of the world? If everyone was doing that, there would be no work to take credit for and economies would halt. Imagine a planet full of conmen, what a great place to live that would be... hmmm... not.
Robert Green indicates some key resources he's used and one to mention is the famous "The art of war by sun tzu" - I believe Robert is extremely interested in books like these and he's only gone and made pretty much, a brilliant book himself.
It's a very good buy, for it's purpose. But can you really find true happiness by being powerful? Well, I'll leave that question for you to perhaps answer, but for me, without any doubt at all, the 48 laws of power is an incredible buy.
I hope my opinion has been helpful to you.