First of all, just read through the credits: Screenplay by BILLY WILDER, Cinematographer FRED ZINNEMANN, director CURT and ROBERT SIODMAK.
Are you serious? This is some serious future talent you have here.
I not even mentioned the naturalistic and realistic filmmaking approach. The Siodmaks used non-professionals as actors and they act completely natural. They're just not trained in theatrical acting so they have to act like normal - and that's the film's biggest strength. I've never seen a silent before that wasn't acted over-the-top (ok, I haven't seen many silents at all) and this acting style was always the matter why I criticized older films (everything earlier than the 50s).
On the other hand, it's a quite experimental take on filmmaking. In documentary style Siodmak & Co. captures the life of five young men and women in Berlin in 1929 - in a time when this very Berlin was one of the most prosperous and fancy cities in the world and just before the Nazis took over power in Germany. This is a quite trivial approach though and although the scenes when our four or five main characters interact work quite well, all the establishing shots just drag along a bit (and there are quite long passages like this).
There's also not really a plot, or a climax, or suspense or any psychological meaning to it hence the (modern) viewer doesn't have much to concentrate on or to give one's attention.
The triviality and realistic approach thus is both the pro and the contra point of the film. Fine filmmaking but not really in a narrational manner.
PS: I saw a very well preserved/renovated version of it - without any music though (which was quite odd). Interesting viewing experience, but as I said not in a conventional narrative way.