Before his death, Marlon Brando recorded a small amount of dialogue to reprise his character, Don Vito Corleone. He was very enthusiastic about this work, was fascinated with the technology involved, and approved of his character's representation in the game. Unfortunately, due to his poor health only one of his recordings made it into the game. The oxygen tank he needed to breathe was audible on the track. The only scene that actually uses Brando's voice was the scene in the hospital. When you approach Don Vito in his hospital bed, he gives a short speech about Sollozzo. Clips of Brando's voice taken from the film are used in some scenes. Doug Abrahams, who also voiced Clemenza and Woltz in the game, was cast specifically for his ability to mimic Brando, and also acted as a dialect coach.
Al Pacino was unable to reprise his famous Michael Corleone character, because he had already signed a likeness agreement with another gaming company for Scarface: The World Is Yours (2006). As a result, EA/Paramount cannot use his voice or likeness for the game. However, since EA/Paramount owns the rights to the Godfather story and characters, the Michael Corleone character does still appear in the game, just with a different look and a new actor, Joseph May, providing his voice.
While the game missions do run parallel to the events in The Godfather (1972), there is one mission that comes direct from the novel. As seen in the opening moments of the movie, Bonasera the undertaker asks Don Vito to take action against the young men who beat and attempted to rape his daughter. Though it's not seen in the movie, in the book, Don Vito has Clemenza's men, including Paulie Gatto, to 'teach the boys a lesson'. You, the player, get to participate in beating the boys.
Because the game takes place in the time period of 1945-1955 in New York, if you listen to the incidental conversation of the people walking down the street, you'll occasionally hear references to the era. For instance, you'll hear a couple of guys arguing over who's a better baseball shortstop, the New York Yankees' Phil Rizzuto or the Brooklyn Dodgers' Pee Wee Reese. By the same token, you'll hear guys say 'I hate the fuckin' Dodgers'. You'll also hear someone say 'Y'know? Truman was the best president we ever had'. Harry S. Truman was the President of the United States during the era.
Not only does Al Pacino not appear in the game, but his scenes are completely cut out of the Unlockable Film Clips. Scenes that featured Pacino fade to black whenever he would have been seen or heard, and then the scene would continue as normal.
Despite the faithfulness the story of the films Francis Ford Coppola, the director of the film trilogy, highly criticized the game's release and eventually denounced it on the basis that he felt the creators of the game were simply trying to profit from his work.
The trivia item below may give away important plot points.
While your character's name is never mentioned (You're normally referred to as 'Kid'), in the mission scene where you and Marty 'Monk' Malone bust in on the undercover FBI agent's hotel room, you can see a Mob "family" tree showing all of the Corleones. There is a picture of your character with a caption beneath that reveals your identity as 'Trapani the Player'. In The Godfather II (2009) it is revealed that the character's full name was Aldo Trapani. Amazingly, one of the Little Italy businesses you extort is called 'Trapani's Bakery' but it is run by someone else and is under the control of the Stracci Family and not the Barzini's who murdered you character's father, Johnny Trapani.