This is an excellent book on negotiation. These are some things I liked about the book:
1) It makes for an entertaining read. Shell uses interesting stories and examples to illustrate his points, so the book never feels too theoretical or academic.
2) It is comprehensive and great for beginners. Part I covers the six foundations of effective negotiation, while Part II goes through each step of the negotiation process in detail. There is even a lengthy chapter on ethics.
3) It provides negotiation advice that is tailored to both the negotiation context (e.g. where your relationship with the other party is important vs where it is not) and the individual negotiator's natural inclinations (there is a test included in the book to help you determine what type of negotiator you are). The latter is particular helpful because most books on negotiation simply teach a particular negotiating style, without considering that a person's personality might prevent him from effectively adopting a particular style.
4) It is well-written and systematically organised. While each chapter is quite long, they are broken down into bite-size chunks through liberal use of headings. This makes it easy to read the book over many brief sittings (as I did). There are also point-form summaries at the end of each section and/or useful diagrams that recap what has been taught.
5) It is intelligent and substantial. Shell brings in insights from psychology (he draws heavily on Cialdini's work) and his job as a negotiation teacher at Wharton Business School, so I never felt like I was reading fluff. And even where Shell's points are not original, he manages to "value-add" by presenting them in a framework that makes them easier to understand and implement.
All in all, I would highly recommend this book to anyone interested in negotiation.