Finished it. Took roughly 27 hours to complete.
From a gamer's perspective, the game is excellent. It has the sandbox crime game thing going for it but the real meat and potatoes is the awesome control scheme.
From a Godfather fan's perspective, the first 3/4ths of the game is fun, as it's a sort of alternate universe where your character was involved with all of the activities seen during the movies. However, when your character becomes the Don, it suddenly pushes aside the storyline completely and you have no idea what happened to Michael Corleone or even Vito, who dies at some point but the player never sees it, only hears about it afterwards. For this reason, I wouldn't recommend it to Godfather fans at all. It's like they had a good lead up, then just fell flat.
I will say, though, that by the end of it, I was glad to be done. It's like Pokemon: I played one game to see what all the fuss was about, but I never needed to play another one.
This will be the same way: I highly doubt I'll ever pick up another sandbox crime game, but it was a fun experience and I'm immensely glad I was able to play one with Wii controls.