Mafia 2 is a beautiful game, but it's failure to innovate pushes it into mediocrity.
One of the worst examples of the above mentioned flaw is the very 'gamey' nature of the missions. In some instances, you are required to go kill a single person -- but you must destroy 100 or more of his henchmen in a long, drawn-out shootouts before you can reach him. This is a big problem not only because it's not realistic to mob life, which the game goes to great lengths to convey, but it's also tedious, and more importantly, it's just not fun. Why not fill that space with character developing dialogue, and a violent execution scene where I could choose how my subject dies (which is ultimately handled in an unplayable cutscene, by the way)? Another example is when you're on a mission to kill someone, you FIND THIS PERSON, and instead of coming up behind them and blowing their head in half with a shotgun and running off (which is what would be true to mob life), you instead tap him on the shoulder, have a discussion with him as to why you are going to kill him (no, seriously), then get in a long firefight with his henchmen before you reach him. Again, this is very videogamey, and competently contributes to steering the game into mediocrity. It also kills the immersion factor. I must've killed almost 200 men in the last chapter of the game, all by myself. Ugh.
While the story itself is likely the game's highlight, the ending to Mafia II is a monumental disappointment. Without ruining it for the few of you who will actually play this game, it's the ultimate cliffhanger, bull**** ending. It resolves nothing, and doesn't even set up an interesting sequel. I actually ended up beating the game again immediately because I thought I may've skipped the ending cutscene on accident the first time (because there is none).
All in all, Mafia 2 may be worth playing on a rental if you are a huge mob-film nut, as there are some nice touches that can be appreciated by fanatics, but for most, it's an average action game in a beautiful wrapping, and very little else.