Mafia 2 it's a 'mafioso' simulator. It's not about story too (although I agree that it is very good). It's about been a mobster. Because of that you're not always in action. Because there is no way the life of a gangster to be 100% shoting. Has the slow moments, small works, days where you just go get a friend drunk at the bar. So the world is huge but you don't fully explored, because nobody fully explore your city. Whether it is the best way to make a game of this type and still make Mi$$ions, that's another discussion. But Mafia 2 is not a game poorly done as they are saying, is simply a matter of choice.
Somehow reminds me of Kane and Lynch 2. No, no, no ... is not laziness of the developers, not lack of time, not lack of money, much less a lack of talent (these guys did Hitman!). The devs simply believe that the best way to engage the player in a "dog world" history is to make the experience unpleasant. Sure, the characters are unpleasant and are in an unpleasant situation. Kane and Lynch are simply sharing their misery with the player. Note that you receive some shots and instead of dying and restart at the last chek point they'll oblige to drag yourself slowly only to die lest than one inch to next cover spot and now you can restart from the last check point. Misery, misery, misery...
I think the big question is. Everyone gets "blablabla game is art, who says the contrary is stupid." But is that really the players are ready to embark on controversial artistic visions?