The absolute pinnacle of studio-system movies, one of the very few that lives up to the hype. The lead performances are both excellent: Bogart does some convincing emoting, and who can blame the DP for all those long reaction shots of Ingrid Bergman?* The supporting performances are all memorable and excellent: Peter Lorre, Syndey Greenstreet, Claude Rains, S.Z. Sakall, Dooley Wilson. The cinematography plays with light and shadows so well, in a way that borders right up on German Expressionism. The plot is twisty but not overly so: it plays straight, with only one flashback, and the character motivations are clear pretty much all the time. It steals one of the excellent scenes from Grand Illusion, to similar effect. It plays dark humor, cynicism, and earnestness all at the appropriate moment.
The energy of the Marseillaise scene in particular seems odd until you realize that the actors and extras drew heavily from exiles and refugees from Nazism, and also if you happen to not realize the lyrics of the Marseillaise are, essentially, "we are going to murder you and your family for messing with us". It's not just defiance, it's an open threat.
This time around, it was easier to appreciate how early Rick starts his plot, and how it depends on playing everyone. It's not always sufficiently appreciated in celebrating this film: Rick's idealism comes out gradually, but his ability to succeed is dependent on his cynicism, not his idealism; it provides the motivation and then gets out of the way. An only-idealistic Rick is going to fail in just the same way Victor Laszlo will fail without Rick, sooner rather than later. The same applies to Capt. Renault: willing to ride the wave of Vichy for as long as it seems like no particular good can come from opposing them and while he can still do some small amount of good (if for selfish payoff), recognizing that anyone else in his role would likely be far worse, and prepared to reject it all at the critical moment because he knows what he should do.
Casablanca is not unlike The Life and Death of Colonel Blimp in its--mid-war!--suggestion that it hardly matters how you come to the right side, so long as you join it, and that success will require both integrity and ingenuity, an insistence that some rules cannot be broken alongside the willingness to bend other of the rules. There's probably an excellent paper to be written on this.
*People are down on Paul Henreid, apparently quite the ass in real life, but I think he realistically portrays someone who is both larger-than-life and monomaniacally focused on his goals. (No one mistakes the figures of Army of Shadows as wooden, though they are similarly opaque.) That's the point of Rick sending Ilsa: Victor does not recognize his own emotional needs, though everyone else does.