What makes the movie "la dolce vita" a classic?

It has a lot to do with the time period in which it was released (1960). During this era, a new form of artistic, neo-realist type of films emerged that changed te way movies were made and viewed. La Dolce Vita was a very early example of this sexual, voyeuristic, fashionable type of film that emerged throughout the decades, beginning in European art films and later coming to America. These films, especially those by Federico Fellini (writer/director), were a huge influence on the American filmmakers of the late 60s and 70s.

The originality of La dolce vita lies in a new form of film narrative that mines "an aesthetic of disparity." Abandoning traditional plot and conventional "character development," Fellini and co-screenwriters Ennio Flaiano and Tullio Pinelli, forged a cinematic narrative that rejected continuity, unnecessary explanations, and narrative logic in favour of seven non-linear encounters between Marcello, a kind of Dantesque Pilgrim, and an underworld of 120 different characters. These encounters build up a cumulative impression on the viewer that finds resolution in an "overpowering sense of the disparity between what life has been or could be, and what it actually is."

The film alo employed several innovative and uniqe technical aspects, such as aesthetic camera angles and shots.