Scratch

I have a general project direction, but I need your ideas. It's called Evolution, and it's basically your run-of-the-mill spy game.
You know, fancy gadgets, cool car chases, infiltration, that kind of stuff. But I want it to stand above the crowd. This is where, if you took the hint, the game 'evolves' to your style of play. More stealthy grants you more stealthy like gameplay, and run-and-gun people will have a more fast paced gameplay experience. But what I am stuck on is how to let you, the player, make this choice.
A Karma-like system, like the one found in inFamous? Or a more linear type style, like the original Driver, where the types of missions you did determined your outcome in the end (the types of missions you do influence they type of gameplay)? Or something else? Also, would you include what type of game? Top-down? Side scroller? Something else? I'm quite stuck, and can't really go forth until I get some feedback.