I guess that everybody guesses what Sneak Mode is all about. I don't think that you will become Sam Fisher but the addition of this feature it's pretty good. This way you can blow a "one hit kill" at your opponent, get more money and steal additional wares or make your way easier into the city.

To keep you well apprised of your sneaky status, there’s even a visual indicator above your target’s head. A green eye, half closed will appear – if you’re in danger of being seen the eye will open a bit and turn from green, to yellow, to orange and bright red if you’re seen. Sneaking is an active skill that you’ll upgrade in game; therefore your success rate is directly proportionate to your skill level.