Casablanca is often considered to be one of the top films to have ever been produced. What merits does the film have that would give it this status?

Spoilers ahead, but then again, who isn't familiar with Casablanca, even if one hasn't seen it?

I've been watching 'Casablanca' over and over again since I bought the Special Edition DVD, and is there any film out there one can watch again and again without ever being tired of it? And does any film appeal to a broader audience? Just everything about it seems to be as close to perfection as it only can be.

But what exactly is so special about it? Is it its great genre mix, never equaled by another film? When we think of 'Casablanca' first, we remember it as a romantic film (well, most of us do). But then again, its also a drama involving terror, murder and flight. One can call it a character study, centering on Rick. And there are quite a few moments of comedic delight, just think of the pickpocket ("This place is full of vultures, vultures everywhere!") or the elderly couple on the last evening before their emigration to the US ("What watch?").

But 'Casablanca' is not only great as a whole, it still stands on top if we break it apart and look at single lines of dialog, scenes or performances alone. Is there any other film which has more quotable dialog than 'Casablanca'? 'Pulp Fiction' is on my mind here, and 'All About Eve' and 'Sunset Blvd.' come close, too, but still I think 'Casablanca' tops everything else. And not only is the dialog great, it's unforgettably delivered, especially by Humphrey Bogart ("I was misinformed.") and Claude Rains ("I am shocked, shocked to find that gambling is going on here"). Many of scenes have become a part of film history; the duel of 'Die Yacht am Rein' and 'La Marseillaise' is probably one of the greatest scenes ever shot (the only I can think of that would rival it for the #1 spot is Wankel and the globe from Chaplin's 'The Great Dictator'), and the last scene is probably even familiar to the few people who've never seen 'Casablanca'. Am I the only one who is absolutely convinced that the film wouldn't have become what it is today if Rick and Elsa would have ended up as the lucky couple?