"Someday they'll go down together
And they'll bury them side by side
To few it'll be grief, to the law a relief
But it's death for Bonnie and Clyde."
I firmly believe that
Bonnie and Clyde is the film that changed American cinema, when the transition from Old Hollywood to New Hollywood was made, and filmmakers have not looked back since (except maybe with the occasional nostalgia). If you look at the Best Picture nominees for '67, the contrast from previous years is striking;
The Graduate, which deals with post-grad angst and the isolated youth;
In the Heat of the Night, concerning racial tensions; and
Guess Who's Coming to Dinner, also concerning the aforementioned topic (a good year for Sidney Poitier, who starred in both, to be sure).
Doctor Dolittle was also nominated, but that was more of a desperate attempt to hold on to the old and cherished than for true merit.