First, it recognises that we don't necessarily need to know all the details of his life. He doesn't bore us with his childhood detail because he probably feels that we aren't that interested in his life in Mid-Texas.
Second, he's written the book in a way that helps us see how he defines himself. He sees himself as a decisive strong leader who knows how to make difficult choices. Consequently he cherry picks the ideas and decisions that might interest the reader (his choices over Afghanistan and Katrina for example), and writes about them at length.
The problem is that this structure doesn't help us much when it comes to understand the man. Just because he wants us to see him as "tough," it doesn't mean he is tough. I'm not altogether sure he is and the book doesn't help me decide about him either way.
The other problem is that it helps him avoid him answering difficult questions. He talks about his drinking, for example, but because he frames it in a certain way, it manages to avoid presenting Bush as a rounded individual. It was just another decision he made instead, and that irritated me some, because I suspect I wanted to see him as a more rounded individual.
I was never a Bush fan, and this book hasn't changed my view, but I do think I understand him better. It's just a shame I don't understand him as much as I could have done by the end of the book.