With this book, I learned three strategy tips the in the first several chapters that immediately made the game more enjoyable and my efforts much more effective against the bad guys.
There are tips sprinkled throughout the book from players who don't work for Ensemble Studios but who are very successful players. These tips were generally helpful as well, and gave some insight into some unorthodox strategies at times.
Shortcuts and hot keys are emphasized and highlighted throughout the chapters. This guide will definitely have you practicing the use of hot keys more than ever (if you don't already).
There is considerable information related to multi-player games as well, such as how to complement your partner and how to know what opposing forces can lend each other in terms of help. I am not sure what the "hard-core" multiplayer readers who rated this book poorly are looking for, but it gave me great insight into being a better team player.
The book does not go into the minute detail of what steps you should takein what order, in every game and every scenario. Certain AOK websites have taken this process to the level of art, and maybe that is what some people are looking for. The book does, however, provide insight into Ensemble's mindset in designing the game and also gives the average-above average player a great boost in terms of knowledge.
If you want to be sure that you are employing as many time-saving tips and shortcuts as you can, and you want to hear what tactics are employed by outstanding players, buy this book. If you are a highly rated Zone player, or can smoke the computer on the Hard difficulty level or above, you probably do not need this guide anyway.
I was disappointed with the "secrets" contained in this book. I'm only a beginner and it didn't really tell me anything I didn't know or couldn't figure out for myself. Some of the lame advice included "use hotkeys," "listen for the audio clues," and "use combined arms." Section on Diplomacy was weak and it didn't really mention how to handle a game against several computer opponents which always tend to gang up on you. Scenario section looked quite helpful if you play the scenarios, but I don't. I would recommend this book for raw beginners, but not anyone above that.