This silent-era classic is an irresistible combination of art and entertainment and an emblematic example of so-called German expressionist cinema which was so influential on Hollywood during the ensuing decades.
Robert Wiene's story of mad-scientist-cum-fairground-huckster, Dr. Caligari (Werner Krauss) and his somnambulist assistant, Cesare (Conrad Veidt, who would later play Ingrid Bergman's husband in Casablanca) who strike fear in the hearts of small German town, is essential viewing for all film buffs who will enjoy comparing it to Fritz Lang's Doctor Mabuse, The Gambler, 1922 (Lang was attached as a director in the early stages of the film and he, rather than the more directorially conservative Weine is generally credited with giving the film its off-kilter tone)
Of course the film is technically dated but even for a general viewer who respects its historical context it is still a very watchable film.
FYI: There are various versions of the film with differing run times ranging from roughly 70 to 90 mins.