Here is an overview and what critics have said about this novel...
A treasure worth killing for. Sam Spade, a slightly shopworn private eye with his own solitary code of ethics. A perfumed grafter named Joel Cairo, a fat man name Gutman, and Brigid O’Shaughnessy, a beautiful and treacherous woman whose loyalties shift at the drop of a dime. These are the ingredients of Dashiell Hammett’s coolly glittering gem of detective fiction, a novel that has haunted three generations of readers.
From the Publisher
“Dashiell Hammett . . . is a master of the detective novel, yes, but also one hell of a writer.” –The Boston Globe
“The Maltese Falcon is not only probably the best detective story we have ever read, it is an exceedingly well written novel.” –The Times Literary Supplement(London)
“Hammett’s prose [is] clean and entirely unique. His characters [are] as sharply and economically defined as any in American fiction.” –The New York Times
New York Times Book Review
If the locution 'hard-boiled' had not already been coined it would be necessary to coin it now to describe the characters of Dashiell Hammett's latest detective story. . . there is plenty of excitement. -- Books of the Century; New York Times review, February 1930