Mikhail Aleksandrovich "Michael" Chekhov was a Russian-American actor, director, author and theatre practitioner. He was a nephew of the playwright Anton Chekhov and a student of Konstantin Stanislavski. Stanislavski referred to him as his most brilliant student.
The first third of this book is worth everything. In it, Chekhov talks at length about personal atmosphere, love in our profession, the curse of materialism in the art of acting, and many-leveled performances.
The final two thirds of this book is not worth much unless you plan on directing The Inspector General (Revisor) anytime soon. Chekhov shows off his incredible comedic instincts and how he plans out physical comedy and, while fun, is not really useful as a window into the Michael Chekhov Technique as a whole.
Even so, there is much in this book that I don't remember reading anywhere else, although I have heard him give similar lectures (maybe the same lectures) in the "Michael Chekhov on the Technique of Acting" audio set.