Let me recommend this an excellent indie game to your attention. Mark of the ninja is a 2D sidescrolling stealth-based game, evoking the glory of games like Saboteur on ZX Spectrum. The player controls a stealthy, nimble assassin whose task is revenge against those who wiped out his clan (yes, unoriginal, but ninja genre is very strict . The game really shines in little details that enhance and freshen the gameplay. For example, your character is fully colored when in the light, but white-contoured silhouette when hidden. Footsteps and other sounds make visible ripples like on water, allowing you to determine when and by who you can be heard. The ninja is ill-suited for direct confrontation with enemies who wield guns most of the time, but especially crafty and deadly when striking from shadows.

Highly recommended!

http://www.youtube.com/watch?feature=player_detailpage&v=o0knqt0qSds