Certain liberties would obviously have to occur in a film version; particularily the sexual nature of the play. But what was also obviousd was that the film would need two major ingredients from the play to be successful, Elia Kazan and Marlon Brando.
Kazan had directed several films already by the time a Streetcar film formulated, and Brando had made his film debut in 1950's The Men. But they would need to return to Streetcar before vitually every door in Hollywood would open for both.
The cast was rounded out with Karl Malden and Kim Hunter, reprising their roles from the stage version. It was detirmined that Jessica Tandy wasn't a large enough name at the time, and so Vivien Leigh (of Gone With The Wind fame) would replace her.
Much has already been said of the importaqnce of A Streetcar Named Desire. Every great actor of the late 20th Century has some roots in this play. This is, of course, due to the profound affect Marlon Brando had on the acting world. His utilization of method acting revoloutionized the future of film acting, which is backed by the likes of Al Pacino and Jack Nicholson.
What I see to be the most culturally significant aspect of this film is the affect Marlon Brando had on America's youth. Without his tough guy role, there quite possibly may not have been an Elvis Presley or a James Dean. Without such names, the rebellious nature of the younger demographic in the 1950s may never have transitioned into the anti-war protests of the 1960s. It goes on an on and I believe it starts with Brando.
Without a doubt one of the most important films in cinema history, and also one of the best.