I prefer Mafia far more than GTA, which I believe is fairly uninteresting, but that is more because of my taste. Mafia would be one of my best games, ever. I have said GTA is crap in comparison before, but they are trying to do different things.
I also fear that they might dumb things down, but if it is the same team and they can fix the numerous bugs of the original, there is a good chance that it will be great.
The late 40s-early 50s is indeed a great setting for this.