As advertised, this is a reasonably nuanced view of Bush's character as it impacts his Presidency. In my view, based upon other things I have read, Draper is probably somewhat kinder to Bush than is warranted.
Draper conducted 6 lengthy interviews with Bush himself, as well as interviews with others in the administration, and these form the basis for much of the material in the book. Based on Draper's Author's Notes, it does not appear that he relied much on interviews or other testimony from non-Administration sources. Since nearly everyone who is or was in the Administration at least started out as a friend, admirer or supporter of Bush, one would expect the picture of Bush to emerge to be more sympathetic than not. And, by and large, that is the case. What is interesting is that, notwithstanding the bias inherent in the underlying sources, evidence of Bush's faults and weaknesses is apparent.
Although Draper doesn't focus on the issue of Bush's intelligence, it does come up occasionally, mostly in comments by others that Bush is not as dumb as is often believed. I've given this some thought over the last few years, and this book as well as others I have read--and my own observations of Bush through speeches, press conferences and the like--lead me to think that, while he isn't "stupid" or "dumb", he is at best a mediocre intellect. That might be fine for an ordinary businessman (although I suspect that Bush never would have been an effective CEO of a real company), but for the President of the United States, it has been close to a disaster.
One of the recurring themes of this book is Bush's observations on the nature of leadership; in fact, Bush seems obsessed with the subject and with performing as a "strong leader". Although Draper doesn't really editorialize on this, Bush seems to have derived his notions on this subject from the matchbook school of leadership. He has an extremely simplistic and superficial view of leadership--it involves never showing weakness and always being optimistic, and it certainly does not allow any acknowledgment, let alone recognition, of mistakes or of the need to revisit decisions in light of results.
Draper also provides some evidence that Bush's management style, implemented by the White House staff, as well as his personality, discouraged staffers from voicing dissenting opinions or bringing to his attention facts which contradict the "group think" point of view. The infamous "Bush Bubble" is in evidence throughout this book, although Draper does not emphasize it.
Draper underplays the lack of intellectual curiosity and the unwillingness of Bush to be engaged by details. Bush, of course, excuses this by referring to his role as requiring him to focus on the "big" issues. But, of course, an effective, competent President must pay attention to detail as well as big issues. What Bush derides as "small ball" is a critical part of governance--making sure that all of the "small" things that government does, it does properly.
This is by no means the definitive work on Bush; that will require the passage of time as well as a broader scope of interviews. However, it is an interesting and nuanced portrait.