Just bought this game the other day, can't wait to play it. The idea of the game is simple, find the people that killed you to begin with. The great thing is to get to that point the options are endless, you can be aggressive and just shoot up everything in your way or stealth your way through the game. Save and help certain people or let them die in order to get to your goal, its entirely up to you. More so certain events may alter due to your actions.
As time advances, these games get better and better and more intelligent. Hopefully at some point these games will involve kinect and the like as to allow for deeper immersive gameplay or more so to allow for facial mapping to give people the option to play themselves in the game.