Williams doesn't shy away from the unpleasant aspects of Chandler's personality and the more squalid parts of his life. The latter part of the book is pretty hard to take, as Chandler becomes a pathetic figure. His alcoholism takes over in a sense, though Williams makes it clear that Chandler had the drinking under at least some control for the best years of his career.
There's no question that Williams is a fan of Chandler's work. He says at one point, "Along with The Maltese Falcon and Double Indemnity, it [The Big Sleep] has come to represent the high peak of the hardboiled genre. And of these three novels, it is by far the best." That's a comment that might draw some argument, but it tells you where Williams stands. I enjoyed his comments on the work, including the rather brief ones on Chandler's early poetry (which was pretty awful).
Williams quotes generously from Chandler's work and letters, and if people who read the book aren't already fans, they might find themselves converted. Check it out.