I saw the movie at the theater when it was released and also played the game on my Xbox 360. To unlock the game extras you had to complete all the difficulty levels of the game.
I still have the Xbox 360 version of the game on my original Xbox 360 Elite, but not the PC version. The game was released, to coincide with the movie, and was an Xbox 360 digital download. If you wanted a physical copy you had to purchase the PC version. PC physical copies seem rare. Would be nice to to have a digital PC copy.