I finished it yesterday actually, took me about 10 hours, I loved it and think it's a great game, but there's room for a lot of improvements. What disappointed me the most is there's no free roam mode at the end of it. The first Mafia game had a free roam game mode separate to the story mode, so there's no reason why Mafia 2 couldn't have it, though I think there's a very good chance they'll add it as loads of people are annoyed about it too.
I'm also disappointed about how much they took out of the game. It figures because apparently there was suppost to be around 18 hours of gameplay, and everyone's not getting more than 10 hours out of it. There is going to be quite a few sets of DLC that add new stories in to the city.
Personally I prefer Mafia 1, though Mafia 2 is a good game in its own way, and has/had a lot of potential to be a lot better.