It’s rare to find a narrative handled so exceptionally well, and it would require someone completely inexperienced to botch it – thankfully, Francis Ford Coppola is anything but. Marlon Brando, Al Pacino, James Caan, and Robert Duvall embody cunning, refinement, devotion, integrity, and ruthlessness in this adaptation of Mario Puzo’s story about the “Corleone” family, a group that begins with absolutely nothing and consequently feels compelled to climb their way to success by any means necessary. The characters are complex and vividly portrayed; Diane Keaton seems completely unaware of the situation she's entering! John Cazale delivers a strong performance as the weak brother, "Fredo," as well. Nino Rota’s score is also remarkable, further solidifying this film's reputation as one of cinema's finest achievements. My only minor reservation concerns the sound; certain portions of the dialogue – particularly Brando’s lines – are frequently difficult to hear.

Source on TMDB