First of all, my child does not have ADHD so I cannot speak about the portions regarding ADHD. Based on other readers' reviews, I sense that the author's views on ADHD have enraged some who have ADHD children.
Consequently, my opinion is that perhaps this book is best for parents like myself with very young kids with "normal" behavior problems that are not rooted in something biological or chemical.
I have a 5 1/2 year old who is very intelligent and can be delightful, but is much of the time whiny, complaining, demanding, and very negative at home. He is horrible at hearing "no" said to him and handling disappointment. On the other hand, at school, he hardly ever gets in trouble, he interacts well with others, and has plenty of friends. My son does not have a psychological condition, but he has been conditioned to act a certain way at home - I will not hesitate to take some responsibility for that. Personally, I felt like this book spoke to my situation.
The book is a fast and easy read. The methods described in this book were easy to understand and implement. Yes, perhaps it's intuitive that we should use positive reinforcement and not focus on the negative, but I will admit that I haven't done that very well over the years and this book gave me some guidance and inspiration.
I love that this book focuses on very young children - i.e., age 6 or 7 and younger, so it felt more tailored to my children. A lot of childcare books out there try to cover the gamut of children from infants to teenagers, and as a result contains a lot of extraneous material you don't need for your own childcare issues.