The winner of both USCF and BCF Book of the year award. It has inspired many writers, most notably John Nunn (see his masterpiece Understanding Chess Move by Move). Although it covers the advances in strategy since Nimzowitsch, one doesn't need to read My System before dealing with this book. Actually, since Watson explains what was the state of knowledge of strategy in Nimzowitsch time, it is a perfect textbook on this subject, far better than My System (which should be avoided at any cost; see my review if you wonder why).
Together with its follow up (Chess Strategy in Action) this book deserves to be in every private chess library.
P.S. For chess players who never heard before (I was one of them, too) about "the immortal overprotection game" Nimzowitsch vs Systemsson, the pages 89-90 will bring them the laugh of their live.