For those that have already begun interpreting why and why they are doing kata, this book is stellar. Much of it is dedicated to the history of our art, explaining why kata developed the way it did. Once you understand a bit about why kata needs deciphering, it makes the thought far more enjoyable. The rules they provide seem very solid, and are backed up with examples throughout the book to help you understand. The edition I read even includes illustrations of many of the techniques.
There's also some bonus material in the book, not directly related to kata. Basic vulnerability illustrations, opponent mindset identification techniques, etc. These are generally brief, and don't interrupt the flow much so they feel like bonuses rather than distractions.
I've created a condensed list of some of the high level points, and am looking forward to trying to use them at the dojo.