This is a film that gets great word of mouth but isn't really all that great. The plot is that Professor Rath (Emil Jannings) gets all stirred up when he discovers his students are going to a local pub to drink, carouse, and get corrupted by the girls. He goes there to have the students thrown out and ends up corrupted himself by Lola (Marlene Dietrich).
Jannings is superb in this movie. His succumbing to flattery is endearing, and his fall from esteem to complete degradation is totally credible. And I think this is the only film I've seen where Dietrich acted. In her American films, she played Dietrich instead of her role.
But Dietrich's role as Lola is truly iconic. _Everyone_ knows the photo of her in her silver top hat, shorts, and garter belt and stockings, looking over her bare shoulder. It's copied everywhere. It's not a major theme in the movie (directed by Josef von Sternberg) - it's just one scene.
The film was supposed to be about Professor Rath, and Emil Jennings was the star. But somehow Dietrich stole the show. Well, not really "somehow" - we know how she did it. Her sex appeal is real, and it makes Rath's humiliating downfall believable. On the whole, the film is a minor German movie supposed to showcase Emil Jannings, and it would have no life at all beyond the early 30s, when it was made. But for Lola Lola.
For an interesting comparison, watch the incomparably beautiful Louise Brooks play Lulu in "Pandora's Box" (Die Buchse der Pandora), a silent film with a similar theme.
(NOTE: Classic Greek tragedy had a hero whose flaw was a character trait that was good, but he took it too far. Oedipus, for example, was curious. He was warned several times to stop asking questions, but he went too far and learned too much. Hubris was one of the favorite flaws; Antigone, for example, challenged the gods to his great loss. After the Greek hero got his comeuppance, the play would wind down pretty quickly. The audience was supposed to feel pity for the hero's tragedy and to feel fear lest we come to the same end ourelves: catharsis.
"The Blue Angel" has some of the characteristics of ancient Greek tragedy, but with interesting twists. Our hero, Professor Rath thinks he has morals, but he's wrong. Instead of going too far with a good trait, Herr Professor fails to go at all. He meets Lola Lola and falls for her right off the bat of an eye. We spend rather more time with our failed hero after his fall than was the custom in Greek antiquity. Von Sternberg dwells on Rath's depths as Lola ceases to be amused by her formerly highbrow husband. She eventually loses all interest and starts an affair with another, younger, stronger man. Rath finds that the depths of hell have no bottom. "The Blue Angel" should have been great, but something failed. My current thinking is that Rath was not heroic; his fatal flaw is not too much of a good thing but rather his lack of real morals behind his facade of righteousness. Perhaps he got what he deserved, leaving me with some pity but no emotional release. Professor Rath does not go down with the honor necessary for a Greek tragic hero, and I think this takes away from the film.)