I've been playing a healthy bit of Mafia 2 over the last couple of days. I'm a little more than halfway through the game, and I'm loving it. I've read some other reviews that are calling it an "empty sandbox" but I disagree with that assessment.
A "sandbox" game, like GTA or Red Dead Redemption is a game whose intention is to give you a whole world to play in. You are, in a way, the god of this fictional city/country. You can wreak havoc on its environments and citizens at will, spend hours and hours off the beaten trail doing side missions or just goofing off.
I don't really get the impression that that was the developers intention with Mafia 2. Yes, the game takes place in an open world, but it seems meant to play the part of another character in the story rather than a free-for-all playground. Mafia 2 is an excellent third person mobster story that is set in a living, breathing city. The purpose is to make you feel like your actions and your story are taking place in a real world, not necessarily to let you go crazy in said world.
The main problem I feel is that Empire Bay is so well crafted, so gorgeous to behold and drive around in, that you can't help but wish that it was just chock full of side quests and mini games and menial tasks just so that you had an excuse to spend more time in and explore more of the city. However, that's not Mafia 2's goal. And it's a shorter experience as a result, but it's no less enjoyable.
Mafia 2 brings a sense of realism in as many ways as possible. From the graphics, which are stunning, to the characters, nearly all of which are well-acted and animated. Driving too fast or running stop signs or mowing down pedestrians will get the attention of the police. Sometimes you want to drive fast anyway, but sometimes it's best to stay under the radar. You're not invincible in Mafia 2, and a frenzied police chase can easily mean death. Not just from the police, either. It is very easy to die a horrible death in a car crash if you're going too fast. Remember, airbags didn't exist yet and seatbelts were only starting to show up in cars. They were death traps on wheels.
The grab at realism and immersion is deep rooted in the story as well. You start each day, generally with a phone call, and you end each day by heading back to your home and going to bed. You'll do menial tasks here and there while on missions. At one point very early on in the game, Vitto attempts to get an honest job, as a dock worker. You spend a few minutes moving crates from point A to point B, all while Listening to Vitto bitch about it. Finally you get fed up and walk off the job site.
Moving boxes isn't exciting gameplay, but the experience really drives home the point that this guy doesn't want to be just another working shmuck like his father. He wants riches and he wants them fast. He wants to be somebody. You want him to be somebody too, so it plants the seeds of reasoning for pursuing a life of crime. The story has a number of moments like this, and while on paper these menial or insiginificant tasks sound dull, very much like Heavy Rain's minor moments, it helps pull you into the story.
The story isn't exactly a mindblowing and revolutionary new take on mobsters... if you've seen The Godfather, Goodfellas etc you'll be familiar with most of the plot devices the game seems to use. But they are all executed so well as to be enjoyable regardless.
With no multiplayer, and a lack of tons of mini-games and sidequests, Mafia 2 is no doubt a short game. There are some collectables (Playboy Centerfolds) which will add more play time if you want to hunt them all down, but realize that this is a tight, well-formed story wrapped up in a solid third-person shooter. It's a great experience, but it's not an incredibly long experience.
I'm playing on hard for as much of a challenge as possible, as is my credo since Demon's Souls, and it's extending the play time a bit, mostly because Vitto dies far more easily, so you have to really make use of cover. I'd recommend it if you want as much out of the game as possible.