If you are at all interested in the history of cinema, or the influence of 20th century politics on the medium, then this film is a must-see, although over an hour of Soviet propaganda is likely to test the patience of modern viewers.
The film's co-director, Sergei Eisenstein, was one of cinema's first formal theoreticians. Quite apart from its didactic purpose (which it renders persuasively, regardless of your personal inclinations) this film is a fine example of his pioneering work in editing. Eisenstein realized that one of cinema's greatest properties was to do more than represent images from life. He reveled in the possibilities of juxtaposition, placing images in rhythmic succession to create meaning (in theory) and powerful feelings (in practice).
Unlike the peaceful resolution posited in Lang's "Metropolis", this Russian film incites righteous indignation by portraying the true story of a sailors' revolt on board the Battleship Potemkin, and the subsequent massacre of the Odessa citizens who had given their support. The story does not give us characters, but broadly sketched social types: sailor, priest, student, mother, and so on.
The sequence in which czarist troops march upon the innocents is one of the most quoted images in film, most deliberately in De Palma's "The Untouchables". This slaughter amounts to a crescendo of gunfire from the ships in the harbour with the town's stone lions edited so as to appear to be rearing up. The effect of this triumph of tempo over plot is an audience ready to yell out "Death to the oppressors!". Assuming, that is, you don't get bored.