I first read this book twenty years ago. The book is not easy to read cover to cover, as has been mentioned by another reviewer, but it is worth working through it. The text often smacks of the evangelical preacher, as do many modern management texts, but the techniques do work. You don't have to buy into the pop psychology, just treat the techniques as tools. The techniques are covered quite briefly, and to make them work in practise takes some effort. This is not going to turn you into a creative genius overnight.
For example De Bono covers brainstorming in some detail, but in my experience in a design consultancy the real secret to successful brainstorming is in the selection of the brainstorm team. No advice on this delicate subject is present in the edition that I read (1969). I found that a sense of humour was essential in all brainstorm team members, as a good sense of the absurd and a willingness to appear a complete as can spark off really good ideas in others.
All in all this *is* a little gem. As far as I can tell all of his subsequent books simply expand and develop the ideas contained in this book. The most useful aspect is in being able to recognise the state of mind where ideas just pop into your head, and in being able to put yourself in a state where this will happen. Some techniques will work for you, some will not. Personally I now use other methods than those listed in the book, but I may not have developed my own way of working without reading this book first.