Note: I want to thank Morticia for re-opening this. I read through the previous posts the other night and thought there was alot left to be discussed. I guess we will see? 
I think the beauty of Casablanca is that it was a "Hollywood" movie, that fate didn't let Hollywood get in the way.
The Film
The film was written, produced and shot as just another part of Warner's factory of films. The budget was moderate, the script was a mess and it wasn't expected to do much. In this current era of movie studios "creating" Academy Award pictures, it's hard to imagine that a film was just plucked out of the general pool of films released.
What's amazing is how much fate kept the film in the fashion we see it. Whether it being an incomplete script forcing Bergman to act ambigious, the build up of WWII bringing the American people to the story, or Bergman having to cut her hair
For Whom The Bell Tolls, to even Selznick's insistance that the film be rushed to print before more changes could be made and the 'Code's' role in deciding the outcome of the film. It was as if chaos created this gold standard of film making.
Cinematography
As for the film making itself, it is top notch. From the incredible detail taken by Edeson to preserve shadows and shark contrasts, it is film noire at one of it's finest moments. I think one of the more brilliant filmed scenes in the movie is when Bogart and Rains go upstairs to get more money for the casino. The camera moves upwards from the side as they go up the stairs, in what is apparently a crane shot of the building with the wall removed. What's amazing is that the scene is blended perfectly into an interior shot of the upstairs office, so much so that it wasn't until about the 15th time watching the film that I realized it.
Script/Screenplay
I'll continue this when I have more time.......