I actually just watched it for the first time a couple of days ago myself. It did feel very familiar, but I think that's because so many things that came after aped it. I'm not well versed in hayes code era films, but I wonder if maybe the derivative aspect you're talking about might be from media made after Casablanca? It was released in 1942 after all.

I thought the movie was kind of mid. Like they tried setting up Rick as this self-interested nihilist but all of his efforts to remain neutral almost seemed like it was played with a wink to the audience. Ilsa was excellent though. Ingrid Bergman melted into the role and you could really feel her tension about her love for Rick and Victor.

As far as Bogart movies go though I still prefer The Maltese Falcon.