Good inspiration for beginners, but with flaws
I am torn about this textbook. There is much to like in The Art of Game Design, and the book is arguably at it's best when Schell relays his extensive personal experiences in the industry. I indeed found some sections to be excellent, for instance the discussions of design principles, of games in education, or or the social responsibilities of designers. I also appreciated the accessible writing style.
That said, as a uni instructor looking for a textbook for undergrad students in a Games Studies course, the book ultimately missed the mark for me. Aside from its excessive length and over-ambitious scope, I found many of the observations poorly reasoned and often grounded in a cursory understanding of related fields. I was irritated by the frequent generalisations about 'human nature', the uncritical discussion of 'player types' (taking the controversial arguments by Bartle at face value), and the frequent assumptions about gender in gaming ('women like to play nurturing roles', etc.). The book would have benefitted from a more careful consideration of the state of the field in disciplines like psychology, anthropology, sociology, and cultural studies. Instead, the author ignores much of the academic literatures, and at one point even derides theoretically-minded work as 'pedantic'. This is a real same, and a missed opportunity.
In short, if you are looking for inspiration, there is plenty to be found in these pages, but for a more critical assessment of game design I'd recommend turning elsewhere.