People reading this book today for the first time may think 'oh this is hackneyed, it's been done before', but what they have to appreciate is that this book started it all. The impact this book has had on pop culture as a whole is immense, from handbags called "The Sam", to remake after remake of movie versions.
The hardboiled cynicism of The Maltese Falcon speaks to our post-modern age just as clearly as it did when it came out. The late 1920s was the apogee of the flapper age. Morals were being relaxed, the restrictions of the past were coming down, people were more free, and that was certainly reflected in Hammett's life and in this novel.
One character that really stands out for me is Brigid O'Shaughnessy. Spade is formidable, and Brigid is his equal, and worthy of this story and this book. Brigid aside, even the book's minor characters are memorable. I loved this curt conversation between Sam Spade and his cabbie:
"The chauffeur said, 'Your partner got knocked off, didn't he Mr. Spade?' 'Uh huh' 'She's a tough racket. You can have it for mine.' 'Well, hack drivers don't live forever.' 'Maybe that's right, but just the same it will always be a surprise to me if I don't."
To sum up: buy it, read it. It's a darn good book.