In my opinion Nosferatu is by far the best movie of German expressionism and of course the best vampire movie. All these kids who watch this Twilight crap gotta spend some serious time in a reeducation camp.
Metropolis is like all Lang-Harbou movies basically a social seismograph, unconsciously depicting contemporary social trends. In Mabuse it is this post WWI nihilism, in M fascism, in Metropolis it is unabashed fascist propaganda (the messianic protagonist who unites workers and capitalists) and in Testament it is a critical view of fascism.
That's why I am not a big fan of Metropolis. It has a few nice scenes, it is not the seminal sci-fi movie it is claimed to be and the the plot is fairly weak and mainly consisting of propaganda. Testament
is most easy to watch for a modern audience as it is to a large degree a thrilling crime piece.