Scorsese's first film, the interesting catastrophe "Boxcar Bertha," marked his birth as a director, but it was with his second feature, "Mean Streets" that we witnessed the birth of an artist. Most of "Mean Streets" is slightly unfocused with a simplistic plot based around a lot of machismo grandstanding and long bouts of boring dialog (occasionally made interesting by DeNiro's off-kilter star-making turn as Johnny-Boy), with spats of visceral violence (far less gory here than in later Scorcese pics), and a visual bravado that seems slightly less disciplined but no less entertaining than your standard Scorsese crime flick.
Despite its drawbacks (mainly due to youth and inexperience), the template was set. The opening credits (done to the tune of "Be My Baby") suck you right into the film, and the rest of the movie is peppered with Scorsese's loving treatment of popular music that would later become one of his most endearing hallmarks. The basic premise featuring Harvey Keitel as Charlie (the young hood with a heart of gold and conflicted internally by the religion of the Church and the religion of the Streets), Robert DeNiro as Johnny-Boy (the equally loved and hated loose-canon brother figure), and Amy Robinson as Theresa (the woman our hero wants to put on a pedestal as a saint but often treats like a whore), is a trifecta of archetypes we see repeated again and again in Scorsese's films (most obviously in "Casino" with the DeNiro-Pesci-Stone characters, and most subversively in "The Last Temptation of Christ" with Jesus-Judas-Mary Magdalene). The religious iconography, the brotherhood of crooks, the attraction to the gangster lifestyle, the keen eye for depicting violence in artistic and startling ways...these are displayed here in "Mean Streets" in their rawest form.
Though flawed in many ways, "Mean Streets" set the stage and laid the the template for the type of film Scorsese would perfect seventeen years later with "Goodfellas." This heralded the arrival of a new talent and a new genre, and the world of film has thankfully never been the same.