The Maltese Falcon is a classic for a reason. Sam Spade doesn't have superpowers. He really doesn't have a special talent or smarts for solving crimes. What he does well is let people run their mouths and eventually tell him what he needs to know.
Hammet describes people and places in minute details. What their expression is, how they are standing, what they are wearing, what they smell like, etc. It's the human relationships that get glossed over in a nudge-nudge way. Did they? Didn't they? The style of writing is much more complicated and dense than the modern mysteries I've read lately. I found myself re-reading passages to make sure I understood them and that was not a negative.
I was in San Francisco last year and it was great fun to recognize the street names. San Francisco was a good setting but did not overshadow the rest of the story.
As for the Maltese Falcon itself? Well, to find out about that you will have to read the book.