Ok I've given this a 3, but, I have to say Yapko has written comprehensively on the subject and that he definitely knows his stuff so in that way his book deserves a 4, or even a 5.
But, (and that's the sort of "but" that negates everything before it) this is such a technical and complicated book that it's not actually all that helpful to the everyday practitioner or hypnotherapist. It reads like a post graduate text book - think of yourself yawning in a stuffy library somewhere in the world. I don't understand why a teacher or communicator would make the subject less accessible in their book.
I'd suggest Ericksonian Approaches instead to be honest.