Sam Spade is one of those characters that make something worth watching, always in control and only showing the people around him see exactly what he wants them to see. The plot's not bad either, keeping various details up in the air, but resolving them before we can be annoyed by that fact. The only thing more I'd want is a little more depth from the other characters, particularly O'Shaughnessy - for a female of dubious morals, we have very little exploration of how that came to be or even her internal life! The themes in this movie have been hashed out a million times since it came out, but there's something a little more true about seeing it in its original form.