This is a great movie!

Rating: Null/10 (4 May 2014)

Spoiler:
The film takes place in the 1940's Mafia era of New York as it follows the Corleone family and their rise to power.
The movie has an award winning cast that includes Marlon Brando (Vito Corleone), Al Pacino (Michael Corleone), James Caan (Sonny Corleone), Robert Duvall (Tom Hagen), and Diane Keaton (Kay Adams– Corleone).
I think the main theme of the film would be power and responsibility. We can see this throughout the film in the scenes with Michael and Vito talking in the hospital, Michael having the bosses killed off during the baptism, and finally the end of the film, when we see members of the "family" recognizing Michael as the new head of the family.
In the beginning of the film, we see that Michael doesn't want anything to do with the organized crime side to his family. We see this when he is talking with Kay, he tells her that it's not who he is. As the film progresses, Michael slowly becomes entangled in the crime side to his family. After Vito is shot and is in the hospital, and Sonny is killed, Michael knows it's his responsibility to watch over his family.
After Vito passes away we see Michael taking control and his rise to power. I think the best scene that shows this is the baptism scene. We see him sitting in the church listening to the baptism, then we cut away to the other bosses being killed off by the Corleone family. You know that Michael is the "head" of the family, but this is not confirmed until the final scene. As the camera pans out, you see members of the family kissing the hand of Michael, acknowledging that he is the new head "Don" of the family.
Even though the film is about the Corleone family, the film focuses on Michael. This focus shows how he changes from a quiet soldier returning home from war, to the head of the top crime family in New York. Another movie where we see this kind of theme, would be the film Goodfellas. With Goodfellas, you see the rise to power of Henry Hill (Ray Liotta) and how he takes responsibility at the end to protect his family.
I think the lighting plays a key role in the theme. Several scenes are shot with low-key lighting to bring the dramatic intensity of the scene. A great example of this would be when Michael, Sollozzo, and McCluskey are driving to the restaurant. The lighting is very low, focusing on the faces of the men. The scene shows Michael meeting on behalf of his family, taking responsibility and trying to stop the attempts on his father's life.
Another technique that plays a key role would be the camera angle. A great example of this would be the subjective viewpoint at Louie's restaurant before Sollozzo and McCluskey are shot. The camera angle puts us in the conversation, showing the intensity of the situation. When Michael shoots both Sollozzo and McCluskey, it shows the power of the Corleone family and Michael taking responsibility to protect the family.
As I watched The Godfather and recognized the theme, I could only sum up the move by saying that "Power and responsibility can be a deadly combination"