Visually it's a great game, but it lacks any kind of substance.
The main story line is good. It's not totally ground breaking, but it's a tested formula that works well for any Mafia game or movie. The acting is pretty decent too.
I like the fact that you can change the cars at the garage. Color, number plates, rims, engine upgrades. You can also shop for clothing which is not only cool but also essential if you become wanted in a specific set of threads and car. Swapping them will set the cops off your trail. It's a good touch, though not something that I was really forced to do on a regular occasion.
There's a fair amount of collectibles. They are pretty hard to find as they blend into the surroundings. They don't stand out like other games.
The Bad: It's actually not that great in terms of game-play. The amount of shoot-outs you have is really limited and can probably be counted on your 2 hands. You're stuck doing menial jobs like taking things from one spot to the next. Killing a guy here or there (which is most of the times a cut-scene in which you have no control anyway.
So not really a great game to play, but the visuals all but make up for the lack of variety in the game.