If it can be done with The Godfather, why not Casablanca? Adventure game a la Grim Fandango (which was heavily based on Casablanca, hell the second year IS Casablanca), maybe with lots of text a la Mass Effect, or it could even be a more action-y Adventure game. Of course, the problem with any adaptation (from novels to movies or from movies to videogames) the developers insist on transforming the material into something that "fits" an established genre. So if it was too much like every other adventure game I ever played, I'd be upset, or if it had stupid "action" missions that had nothing to do with the main story, I'd hate that too. Maybe it should be a Rashomon style game that tells the story from different perspectives (Laszlo, Rick, Ilsa, even Ferrari, Ugarte, and Captain Renault). That would be really awesome if it was done by someone with talent (Tim Schafer?).
But most of all, I'd want this game made because it would be in black and white.