I enjoyed David's Principles of Bonsai Design. As I have been practicing the art for a few years, I have been looking for books that have something 'more', and I feel I found it in this book. David spends a lot of time on differing styles, especially some that aren't traditional, or 'accepted' styles of Bonsai.
I also appreciated the sketches and pictures within the book, though I will say some of the photographs were a little on the 'rough' side though, and could have used some additional touch-up before inclusion in the book - things like color/contrast and quality.
I was surprised by the many pages dedicated to Chinese Penjing. While Bonsai is of course descended from Penjing, usually there paths do not cross to this great of an extent within a book. It was very interesting though to learn more about the styles and concepts behind Penjing, which many times differs widely from Japanese Bonsai.
Overall, I do feel I picked up some new tips on the styling of Bonsai, past what I have read prior. I suggest this book to any others who have been practicing the art for some time, hopefully you too will find some new tips. The book though is not for novices, or those just starting to learn of the art, as it spends time on the concepts of styling Bonsai, and doesn't go into detail at all about the horticultural aspects of keeping living plants alive.