Why do the films we love improve to us with subsequent viewings? Good question and I'm glad I asked it.
The first time we watch a movie it's to follow the story being told. Our view is rather flat, akin to listening to a song and just hearing the lyrics, not being quite aware of the phrasing or the instrumentals. It is with second and third viewings of a film that we start to appreciate how the story is told.
Notice the uncrinkling wrapper on the counter top in No Country for Old Men, why did the Coens focus on it and isn't it interesting? The iconic opening and closing shots in The Searchers are more poignant with each viewing. The faces in the streets of Vienna in The Third Man become more interesting. The interplay between Jean Harlow and Clark Gable while Harlow bathes in Red Dust. The rain in the Big Sleep. The dark wet mood of Blade Runner. Note the relationship in To Have and Have Not between Bogart and...Walter Brennan (you thought I was going to say Lauren Bacall but the Bogie/Brennan dynamic is worth following too). Stanwyck's seduction of Fonda in The Lady Eve (Sigh!).
Great films have great moments, great relationships, great cinema photography, great vision. In any good Cagney movie you start to notice his hands, like the way he rubs them together in Roaring Twenties or the way he touches Blondell in Blonde Crazy. So precise, so delicate, yet so masculine and confident. Like Burt Lancaster and how nimble he is on his feet. Lancaster was about as graceful walking as Astaire was dancing. In the really good films Cagney and Lancaster's physicality become all the more significant and pleasurable.
You also pick up sounds with increased viewings like the way Woody Allen uses music, I don't know that any director does it better. Or the ping of the sonar in Das Boot or the sound punches make in Raging Bull.
Movies have too much going on for you to be able to pick up everything one time through. A movie that has a good story to tell and tells it well is worth repeat viewings. You see camera angles and actor's mannerisms, you hear ambient noises, you understand director choices. In other words you start to appreciate why the story was so compelling the first time.
Yes it's nice when films aren't formulaic, but all the originality in the world won't save a film unless its told in an original interesting way.