I think to an extend that this book has been overlooked because the movie is so good. Hammett's original book really is a spellbinding read and was difficult to put down. It's refreshing to remember a time when mystery and suspense writers had such a wonderful mastery of language.
The only conceivable flaw for the reader is that so many of the characters and settings have become token or stock characters since it was originally published. The thing to remember was that it started here.