This is a very opinionated book. It tells parents exactly what to do, with little in the way of reasoning, let alone evidence. Often the advice seemed like common sense, e.g. giving a child a chance to do better as soon as possible after being reprimanded. That can still be useful, since even when the book gave advice I already agreed with, I often noticed afterward that I wasn't following the advice as often as I'd thought. Other times, though, the advice went against my common sense, such as the advice to discourage tattling even in cases where you agree that you need to intervene. In those cases, I didn't get much out of the book, since no attempt was made to change my mind.
This is a very practical book. It doesn't just tell you broad outlines of what to do, but rather goes into a lot of detail. For example, lots of parenting advice suggests sticker charts, but this book goes into a lot more depth than other sources, listing common mistakes parents make using them and how to avoid those mistakes.
This is a very comprehensive book. I was expecting a book on effective punishments, but it covered a lot of other aspects of parenting too. It was focused on how to get better behavior from children, but within that focus it covered a side variety of techniques - time outs, ignoring unwanted behavior, positively reinforcing wanted behavior, teaching problem solving skills, etc.
Even though the book doesn't feel evidence-based while reading it, it is evidence-backed. I picked it up because Emily Oster mentioned in Cribsheet that RCTs have shown children's behavior improves after parents take The Incredible Years course. The studies looked at a live course, but presumably the same topics are covered as in this book. That does help a bit forgoing judgment when I disagree with the book, although I would still prefer more reasoning to be given.
The cover of the edition I read says it is for children ages 2-8 years. Earlier editions said 3-8 years, and I think that was more accurate. I don't expect most of the techniques here to apply to my 2 year old for anothet year or more. Thus, I can't yet directly judge the helpfulness most of the advice. However, my initial guess is that in a couple years I'll be glad I read this.