The Big Sleep is far and away my favorite detective movie, certainly of the classical era and probably of all time. What separates it from all the others is that it doesn't rely on the mystery to at all be what holds our attention and entertains us - it's all in the banter and the characters. It's quite literally style over substance, and it's a more wonderful film for it.
This is sort of how I've come to approach some of Jean-Luc Godard's films on a first viewing. I have no idea how anyone could come to any sort of concrete understanding of Pierrot le Fou or, indeed, Made in U.S.A once through; they're absolutely packed to the brim with references, allusions, and hidden meanings. Never mind the rather esoteric nature of the plot itself. What I do know is that, with each of them, my first viewing has been immensely pleasurable, purely through the rhythm of the dialogue and Godard's camerawork, defined by incredible set-ups, thrilling tracks, and hypnotizing length. And color...oh what color.
I missed the days when color and monochrome were each viable options for filmmakers, and what stock they chose represented a decision rather than a default. One of the reasons the 60s is perhaps my favorite decade in film history is because it represents a rather narrow window of time in which that choice did exist - before that, color was too expensive, and after that, it came to be something that turned audiences off. Films like Made in U.S.A earn that decision to give us all the color of the rainbow and more, and as we've never seen them before.