This is the kind of book my doctor advises me to read, it's a very good reference, as well as Dr. Thomas Brown himself for his work in this field. I was pleasantly surprised to find out I had been lucky enough to read it before contacting my doctor, I had been searching in the right place, thank God.
For someone who wants to understand thoroughly AD/HD this is a must. Probably not as down to earth or apparently simple as some "practical" books you find here and there, but that's mostly because of some sections where the whole chemical or structural process is explained. He makes more of a medical approach to the problem. Yet, the personal experiences he uses in the book help us a lot to see how that affects real people, in common day to day situations. Sometimes amusing, others dramatic or even tragic.
In my opinion, you may find very useful to read this book plus Edward Hallowell's/John J. Ratey's "Driven to Distraction" and "Delivered from Distraction". These last two's approach is slightly more simple and will help you to get a wider perspective.
I guess Dr. Brown's seems to be more complete and structured for someone who wants an acurate understanding of this issue, but I think they actually complete each others.