To be quite honest, I have never seen what the big deal about Casablanca is. I hate to say it, but I think it's one of the most overrated movies of all time. I understand the historical significance of it and know it was the first movie made about World War II and made during World War II and the script was apparently written as the movie was made.
I wouldn't say Casablanca is the best classic film, but if you're comparing it to the nonsense being made these days starring Ben Stiller or the drivel Adam Sandler is producing for Netflix, then yeah Casabalance is a damn masterpiece comparatively.
Taste in movies is subjective. I am not saying Casablanca is a bad movie, but it is overrated. Many people who list it in their favourite movies ever list are usually just hipsters following the trend of having to "love" classic films because it's the hipster thing to do.
Don't get me started about Donnie Darko...