Its purely underrated. This is by no means a bad game.
The storyline is not worth talking about. It is quite disappointing because The Godfather both film and game had great narrative to them. It looks like they canned the writing studio at EA when they were developing this game.
The gameplay is repetitive but it is rather fun playing a don. I really enjoyed beating business owners to get a deal from the them. You can have a group of men do task's for you and they work fairly well. It makes the game too easy though.
There are a few bugs in this game. You can watch your crew run around a physical object for hours, you can sometimes see freezing and you can still always get shot in dialogue and you are still stuck in it and can die quick. Most bugs you do not notice until a critic points it out and ruins the game experience for you.
This game is a 'Rent' if you so need to play it.