I found this book to be too superficial to be life-changing. The message boils down to "having a big, long-term goal can lend order, structure, and purpose to your life, which in turn can make you more satisfied." OK, good premise so far. But the book lacked any deep exploration of the hows or whys, the practical steps to finding and completing this quest that is supposed to make your life so much better. The book tells the stories of dozens of people who pursue a range of different kinds of "quests," but really focuses on the adventuresome quests: the man who walked across the United States, a man who bicycles around the world. The less-athletic and far-flung quests are not given as much discussion, which I think is a real weak spot for the book. Not every reader wants to (or is physically able to) walk across a country or climb a mountain, which the author recognizes but doesn't adequately expand upon.
I also have issues with the author's definition of a quest (given in Chapter 1, page 15 in the edition I read) as something with a clear goal or endpoint. More precisely, I have issues with the fact that the quests discussed in the book don't all meet this definition. For example, the author discusses a man who stops using motorized transportation and stops speaking for 17 years. He did have a clearly articulated motivation for doing these things, and he certainly faced challenges and a lot of personal growth, but the description of his "quest" doesn't demonstrate that he had a clear goal or endpoint in mind.
I also disliked the author's characterization of "[q]uitting smoking, losing weight, or getting out of debt" as not quests because these actions "shouldn't be a lifelong focus." I can see why the author wouldn't want to write a book about something that literally millions of people do, but that doesn't justify their dismissal. All of those things can meet the definition of a quest that he subsequently lays out: having a clear goal, requiring sacrifice and incremental changes, facing challenges, and spurring personal growth and discovery.
I understand why this is not a book about the mundane goals and challenges that everyday people face (because I doubt that such a book would be a best-seller), but the the larger than life tales of epic quests don't really spur me to go on a quest of my own. If this book were more focused on applying the lessons from the big quests (the goal setting, the need to step outside one's comfort zone, the self-reflection and acceptance of challenge or defeat, etc) to everyday life, perhaps I would have enjoyed this book much more. But as it is, it is just another rather forgettable self-help book.