My guess is what several others have said - weak - easily manipulated - superficially "nice" - narcissistic - manipulative - lacking a "center" and possibly quiet dangerous (to us who attack his narcissism) - and possibly not.
In some ways we're back at square one. One new concern - it was too easy for him to lie about writing the book. That's bad. Knowing what we know, I'd like to know who is the person behind him... Ayers lacks the self discipline - so it's not him.
If you think about it - you know who Obama is. But you have to believe your lying eyes and ears rather than what comes out of the mouths of the GOP and DNC.
Bill Ayers wrote the book using Obama notes and only occasionally put in his own experience to juice up the book. The book was not about Ayers except in rare instances.