It would've been rated much higher if it wasn't called The Godfather.
Well, it plays good. The Gta aspects work mighty fine although the atmosphere doesn't come close to any game of the Gta franchise. The streets do not seem alive and all NYC looks monotonous and boring. Although the overall sight of the city does a good job of imitating the time period.
The gunplay is also quite good. The auto-aim system, although doesn't feel necessary, is a welcome addition because the game is quite difficult. Added checkpoints (take that Gta) feel like a blessing but the game still seems to difficult.
The Godfather implements a couple of new features to the traditional sandbox. One of them is negotiations with shopkeepers: you have to pressure them to pay protection money by smashing up their shop and threatening them. It works although the negotiations do become tiring after a while. There are also gang war periods but, quite frankly, they don't accomplish anything.
The main downside of the game is its license. To be exact, how it handles its license. The Godfather movie didn't have a lot of shootouts or even bullets fired. It concentrated more on the life of the family, the negotiations, the decisions. The game neglects everything established by the movie. You are constantly shooting people. Important characters flash before your eyes and then get killed afterwards (most likely, by you). It could've been forgiven since the protagonist is just a regular soldier for the firs half of the game but the way it deals with the characters (or with Godfather continuity) is unacceptable.
If you want to play a good Gta clone, by all means, do so. But if you want to see the movie from a different perspective and take part in its events, look elsewhere, because Godfather The Game is just a shallow rendition of Coppola's masterpiece.