Firstly I've not played the original Mafia. I thought this was a real mixed bag.
Game starts off very well, the atmosphere when you first arrive in the city, the attention to detail is brilliant. But no sooner has the game started those little details just stop. When you first go for a walk there is a couple arguing in the street about their broken car. If you hang around the husband walks off and you can fix it for the woman and she thanks you and drives off. There's only three of four more times this happens in the game and never to this extent. It's these details and side missions that make the city feel alive.
One of the stand out moments in GTA4 was me standing on the terrace outside PlayboyX's apartment in the early hours listening to the traffic and police cars on the streets below, the city felt truly alive, that around the city events were taking place without me witnessing them. In Empire Bay I never had that feeling, when I turned a corner in to some street and saw a pedestrian slip over on the icy 'sidewalk' it felt like he'd been waiting for me to arrive. The lack of of public transport is also really odd, there's raised railways, and stairs down to subways, not to mention bus's and taxis, and you can't use any of them! As I posted on twitter last night "You can flush the loo in your house, but you can't hail a taxi driving down the street!"
Story was solid enough, with some twists and turns along the way. I did wonder about after being in "the faaamilee" this group of 15 people who were supposed to be loyal and caring more for each other than their own real families was happy for me to be living a filthy flat.
The game engine is quite impressive, the softening of distant objects gives the city scale. Architecture of the 40s and 50s, exteriors and interiors are very good. As someone above said, the cars felt very heavy and travelling 100mph in one felt like an imminent death experience. Music was good, but towards the end I was getting a little irritated hearing the same stuff over and over again.
I'm expecting a lot of DLC for this, whether I buy it is another matter...