I really enjoy Hammett and feel that he is far superior to his closest alternative Chandler who is all style and no substance. The story, like the works of Fleming, is really all about the subtext.
What makes this book great is the last 40 or 50 pages. Hammett has something to say about the human condition and combines a deep cynicism about human beings with a commitment to morality that necessitates an individual ethical ideal. In this ethical schema, people who are moral exemplars must live by codes of their own choosing because of the inherent immorality of the world and as such be very much alone. That view is very much in place in Hammett's works, and as such beneath the detective story there is both a melancholy but also a commitment to an ethical code. It is a code where the ends very much justify the means. It is very like the films of Kurosawa in this regard. It also necessitates a cynical world view. The hero must have no illusions about the world in which he lives or the characters he is trying to save or he will fail.
What I think is interesting about this book is that when you read the other reviews of it, the subtleties of Sam's Spade's character are completely missed in most of them. This may be why Chandler is generally preferred, because Chandler's one liners are better, even though Chandler has nothing whatsoever to say, whereas this book is a meditation on how to be moral in a fundamentally immoral world. Funny that Sam Spade is seen by so many people as an immoral asshole. I would have thought that the last two chapters make it clear that he is not.
Very good. Everyone should read it.