Pain Free is the simplest, most direct explanation of the Egoscue Method available...if you'd like to save hundreds if not thousands of dollars over therapy, get this book.
Pete Egoscue deserves enormous credit for introducing the concept that structural integration - aka postural alignment - is the primary method for relieving all kinds of chronic pain. Western medicine is fantastic at combating "acute" problems (broken bone, heart attack), but has not traditionally been so great at tackling "chronic" problems... something that I think postural alignment really addresses much more effectively than most western physical therapy. I personally thought so highly of the Egoscue Method that after I bought and read this book I went to get treated at an Egoscue clinic (where I think they correctly diagnosed my problem), I bought his two other books, took the P3 seminar to get their lowest certification, and referred my dad and a good friend to Egoscue for their problems.
I would say that the biggest criticism I have of Egoscue is the time required to do the "e-cises"... these can literally demand 30-45 minutes PER DAY to apply appropriately. Also, Egoscue's depiction of the ideal posture, which I originally accepted as gospel because I had no comparison, I have since come to think of as slightly flawed.
I prefer Esther Gokhale's "8 Steps to a Pain Free Back" for two reasons:
1. It takes MUCH less time - you simply learn the Gokhale method and then integrate it all the time without separate exercises.
2. Instead of trying to figure out from an engineering perspective what's best for the body as Egoscue has done, Gokhale went out to indigenous peoples with very low incidences of chronic pain and simply observed what they were doing...her depiction of the ideal posture is based on this, and is what produces the slight variations with Egoscue's ideal posture. I think Gokhale makes a convincing case for her method because of this.
If you're sold on the Egoscue Method, then I highly recommend "Pain Free" as the book to get at the method the quickest (well-done book with illustrations and explanations); but I prefer Gokhale and would recommend checking that out as well.