The way mathematics should be taught. Most math teachers really don't 'get' math, they know it, but they don't really know it well enough to explain it from the ground up. In this way Crowhurst's math books are very much like Feynman's physics. He understands the subject so well that the complex topics become intuitive. These books have helped turn my child from a math-hater to one who is taking a math minor in university.