I spent several hours choosing a game design book, and from the other reviews I figured thi must be the one. However, I discovered that it reads much more as a theoretical textbook than a practical guide. Mind you - I have a Ph.D. in IT so theory is great, but only when it's actually useful for something.
If you want 7 definitions of "what is a game" and an in-depth discussion about what is a rule and what is not a rule, spiced up by discussing how Tic-Tac-Toe permeates and influences the contemporary culture, you're going to be satisfied. If you wish to learn how to design games, you're also going to learn quite a lot but on the way there you'll have to skip quite a few sections of this hefty tome.
I bought
The Art of Game Design: A book of lenses at the same time. Although my focus is not on digital games, the Book of lenses is so much more practical and inspirational that I just have to recommend it, along with
Challenges for Game Designers which may not be as inspirational but is all the more practical.
Hope I helped :o)