Despite the staggering possibilities for violence, you'll need to keep in mind that you're a representative of the Corleones, a gentlemanly, old-school Mafia family. As such, you're expected to keep your business private. So while Grand Theft Auto -style rampages and flashy massacres are possible, they're discouraged. Cap too many civilians, and the cops will start attacking you on sight. This goes double when dealing with rival gangsters, who don't take kindly to seeing you on their turf and will hold grudges for every one of their boys you humiliate or kill.
Throw in some driving, lots of gunplay and performances by James Caan and Robert Duvall, and The Godfather looks like one hell of a promising movie-to-game adaptation. Look for this one later this month.