The acting/writing was pompous, actors talked like reciting Shakespear. The movies were about heros of impeccable character doing heroic things and there always was a happy ending. Movie shots followed strict guidelines and the creative head of the movie was the producer while the director was akin to a contractor, someone hired to film the scenes.
Starting in the mid 60s there was a radical shift, topping the nominations we have films like Five Easy Pieces, The French Connection, The Godfather, One Flew Over the Cuckoo’s Nest, The Deer Hunter, Dog Day Afternoon, Taxi Driver etc. Actors would act and behave like normal everyday people facing everyday problems. The new Archetype is the Anti-Hero, someone with flaws/vices in their character, someone that viewers can relate to. We see the rise of the director as the auteur, the creative master of a film. Every known filmaking rule is being tested to it’s limits and broken by young experimenting directors.
The catalyst for this change was the French New Wave, a group of young filmmakers tired of the old style of cinema wanting to do films about their own life and experiences. The poster boy for the New Wave was Jean-Luc Godard starting this revolution with his 1960 film Breathless.