I thoroughly enjoyed Mafia 2 while it lasted, but after completing the game in 10-11 hours there was just nothing left to do. No side-missions or collectables...
The story, the graphics, the driving mechanics, the shooting mechanics... all work well. However, once completed you are unable to go back and explore the city without reloading a previously-completed chapter. This wouldn't be too bad except your saved game then reverts back to that chapter, so you can only play subsequent chapters by playing the game through again.
Frankly, I couldn't be bothered.
I was looking forward to driving around, admiring the views, exploring the hills and areas where the story never took me, tracking down the 50 Playboy pictures (turns out you have to do that while in the storyline) etc etc, but you can't.
Perhaps the developers are relying on DLC to flesh the content out but that's not what I expect when I buy a game and, to be honest, I find it a bit offensive.
So, I recommend the game, but it may be worth waiting until the price comes down a bit or you can get one second hand. £40 for 10 hours gameplay just isn't worth it.