In a preview in Games Radar this can be read:
In spite of all the ridiculous levels of detail, though, Mafia II - like the original game - will focus more on telling a linear story than on open-world freedom.
For me this is good news since the story in Mafia was so interesting and complex. Those who want total freedom can go to Freeride or buy GTA IV instead.
I think most Mafia-fans agree with me on this.
The whole preview: