it is readable (and a pleasure to read) while being informative.
One of the problems with XP is that many programmers simply dismiss it as a mirage. The people who do this are often among the better programmers who know about process and how a development project should be organised. When they read about XP it sounds to them like their worst nightmare of a bad development process.
Let me be honest, I think XP is hyped, and is far from being a silver bullet. However, I also think that it is a valid development method applied to particular kinds of software. Specialist, one-off, business software is often well suited to the XP process.
Rather than teach you what XP is (others have already written such books) the authors of this book have effectively written the biography of the development of a particular piece of software using XP as the development process.
The actual software was to handle registration of visitors to the company's web site, and to do so as unobtrusively as possible. How well did they succeed? Well you can judge that by visiting Object Mentor's web site.
This book is about how they produced the program. Like most of the books on XP, it is readable (and a pleasure to read) while being informative. You are not required to use XP yourself, but this book is the story of a group who did use it and what they experienced as a consequence.
If you are willing to suspend your own religious beliefs as to how software should be developed, this book may make you think and possibly broaden your horizons. If you are already a devotee of XP (Microsoft should be sued for appropriating that pair of letters) you may enjoy reading about and learning from the experiences of another team.