Schaller's sublime style of rendering is reason enough to buy this book (and perhaps to clip the pages and insert the images into frames that once hosted pictures of your relatives!)
Watercolor is a difficult medium, and this guide, if it was intended to be such, does not serve the beginner well with introductory techniques. However, it does portray stellar examples of watercolor rendering, and a study of Schaller's work can reveal graphic composition/ and color techniques to complement any renderer's toolbelt.
His examples show artistic use of depth, composition, foreground-background balance, dynamism, and shadows.
I've always read the word "spellbinding" in reviews. After this book, I know what that means. I am surprised, after reviewing Schaller's work that he is not renowned as an artist outside the architectural sphere (at least to my knowledge).