This book in my opinion shouldn't even be published or sold. It's highly controversial and has attracted a lot of criticism from pediatricians. It advocates practices that are unsafe for infants and there have been actual cases of infants having health issues as a result of parents following the advice in this book.
I found this book great! It advocates that a parent needs to be the one in control and direct their child to establish a flexible routine. It does go against a lot of common advice (such as demand feeding) - but it makes sense. My daughter was sleeping through the night at 9 weeks thanks to this advice. That meant I got more sleep and so did she. She gained weight readily and is now a contented and well-behaved 18 month-old.
I loved this book. It is not a Bible but gives some very good advice - you don't need to do EVERYTHING it suggests but the theory behind the book - establishing a flexible routine and not demand feeding is excellent. Both my children slept through the night early on and it gave me assurance!