This is a difficult book for me to review, because as a D&D nerd it's hard not to have a lot of Opinions on it. My inner geek found plenty of nits to pick with this book: annoyance with the casual dismissals of the versions of the game the author didn't personally play (2nd and 4th edition, primarily) and a wish that the author would have dived deeper into some of the historical bits (the whys and hows of the 'satanic panic' of the 80's are skimmed) are chief among them. The post-Gygax years of TSR and the release of 2nd Edition or any setting the author hasn't played (Forgotten Realms, Dark Sun, Eberron) are also conspicuous by their absence.
So let me review this as a writer. From that perspective I also found this book somewhat lacking. The author centers the book around his own personal journey with tabletop roleplaying games. Chapters alternate between the history and business of the game and the author's own stories. The latter are interspersed with dramatic prose-style descriptions of games the he has played in. At first this is fun, but it quickly wears out its welcome to the point where I found myself skipping the endless paragraphs of italicized purple prose. What works well for, say, the read-aloud text for a D&D campaign is tiresome in a non-fiction book.
And while I understand the David Ewalt is using his personal experiences to make the topic accessible, it has the result of making him the main character of this book. And he's one I tired of quickly.
There are also the cliched 'lessons to be learned' from every single experience, something that really annoys me in non-fiction books. In life not every event is pregnant with meaning. Attempting to find personal revelation in everything just to fit a narrative feels extremely forced, and Ewalt does this in spades.
Finally, and I just have to get this out there, as a Fourth Edition player it's clear to me that the author has never so much as even skimmed a rulebook, and is going entirely off what he's heard and read elsewhere. Some of the things he was oohing and ahhing over about D&D Next had me rolling my eyes. "Yeah, you could do that in 4e dude." I will grant the author his personal preferences, but I think if you're going to write a book about the history of D&D you could pretend to have at least a modicum of objectivity.
Nerd wars aside, I did learn some things. Ewalt does a good job introducing us to the personalities involved in creating D&D between 1970 and 1980. Gary Gygax, Dave Arneson, and many of the lesser known (but still important) players get full treatment.
For someone looking for a light, quick introduction to what Dungeons & Dragons is, how it got started, and why it's important to millions of people the world over, this book is probably worth picking up. But if you have more than a passing knowledge of the game, you can probably safely skip it.