Deus Ex : Human Revolution.
Great game, I had this game when it came out for 40 Pound, and it is well worth that price. For 17.99 this is an absolute steal. Great mix of Stealth with a little bit of Gun mayhem thrown in. I will warn you, this isn't a 'run and gun' First Person Shooter outright, you can go Gun(g) Ho but it pays to assess the different aspects of approach to each situation.
Enthralling storyline, great voice overs will immerse you in this beautiful bargain of a game.