The revised book is mostly the original edition with 400 extra photos and some additional new content. I would definitely advise buying the revised version if you have the choice, as the photos add another layer of explanation/demonstration. The format of the book follows a logical progression in 11 chapters:
The Enlightened Approach
Position and Balance
Interacting with the Horse's Movements
The Aids-an Explanation
The Application of the Aids
Understanding Schooling Terms
Turns and Circles
Transitions and Half Halts
Rhythm and Expression
This time around when it came to implementing the step by step instructions I found everything easy. So why, this time, when I came back to this system of learning dressage did it work so well and clear up several things that I have struggled with including turning and bend? I think it is because in the intervening years I have figured out the importance of waist to hands/pushing into my vertical powerline/using my core from my seat to my collarbones. With that in place everything else in the EE approach worked really well for me. Heather includes a short section on the importance of having a strong frontline/core but she doesn't go into a lot of detail and I never got that I was missing that piece of the puzzle when I tried EE years ago. All of the photos and videos of riders trained by her show riders with superb posture, so I think it is a matter of if you ride with her or one of her instructors they do emphasize pushing into the frontline, but if you just read the book and didn't have knowledge of using your frontline you can easily get stuck. When I came back to EE after having read When 2 Spines Align(vertical powerline)and The Classical Rider(ride the crest of the wave) my core/frontline use was good and everything and I mean everything in the EE approach worked really well.
So, I personally would like a little more emphasis on use of the core/frontline in the written EE approach since it would have saved me years of wandering in the wilderness BUT pretty much everything else in this book is spot on. It has cleared up many aids and movements that were close but just not quite right. The progression of exercises works really well for a non-Warmblood type of horse as well. The explanations are clear and easy to understand. Supplementing with free Heather Moffett videos from YouTube also adds another layer of understanding. I have found this book super helpful at this stage of my riding career and I would highly recommend giving it a read.