The Cabinet of Dr Caligari was a huge international hit on release in 1920.  For the post-war German film industry facing a hostile international market, this was a huge commercial achievement and led to a decade of innovation and creativity in Weimar cinema.  A huge influence on both the art film and the horror genre, Caligari is a tangle of contradictions; a blockbuster that became an essential text in the history of cinema.
You can find my analysis of another Weimar classic,  Nosferatu at Nosferatu: Analysis of Film Form, Auteur C...