The romantic story of hunting for a lost jewel and the rough hard-boiled detective don't go well together. I kept expecting a note of common sense to appear, as for example, it would be real fun if the gambler's war theory turned out to be true, and all the trappings were just so much dramatic fakes run up for the benefit of the naive sleuth. So here's another jarring note: he isn't naive, why the heck does he swallow all the falcon talk without any apparent scepticism?
To this inherent flaw in the conception add the flowery prose, the inexhaustibly detailed descriptions and the thin character interaction, and I can see why the movie is so much more popular than the book.