For a 2010 game, the graphics leave a bit to be desired. The loading of a save game BEFORE you start the story mode is a little clunky until you get used to it. You can't save your progress, the game does it automatically for you, which again is quite unlike other open-world, mission-based games.
Then again, Mafia II may be open-world, but it's certainly not sandbox. It's an on-rails, linear shooter. You go from one mission to another. There are NO side-missions, which feels like a massive opportunity lost. Early in the game, you're introduced to characters like "Bruski" who apparently always have jobs to give for money, but this character never gives you a job at any point, ever. It feels like the developers wanted to do so much more, but either chose not to, or ran out of resources.
That being said, it's difficult to find many flaws with what the game sets out to do. The story is engrossing, the voice acting is pretty good and the gameplay is hugely enjoyable. Shooting is fun because all the guns (especially the Tommy gun) feel powerful. The game forces you to use the cover mechanic because Vito (the character you play) is as vulnerable to bullets as his enemies are. Stand exposed for a few seconds and it's quite likely that your screen will lose colour quickly.
I thought driving would be a pain in the arse because 1940s/1950s vehicles are not just pretty slow, but also difficult to control. After almost every mission (especially in the first 2/3 of the game), you need to drive back home to sleep. This may sound boring, but surprisingly, I didn't find it particularly boring. There are 3 radio channels, and the scenery is nice. Plus, there's a bit of challenge thrown into the mix where you have to ensure you're not crossing the speed limit in view of the police. That added tension (however mild it may be) is enough to make sure the driving doesn't get particularly boring.
The supporting cast of characters is great. Joe (Vito's best friend) initially comes across as brash and not very bright, but as the game progresses, he shows a high level of aptitude for criminal thinking as well as execution. Most of the other characters are well voices, the accents understated.
All in all, a fun game. Might be a little too easy in large parts (and I'm sure most people would find it easy), but it's a great experience.