Ninjas may be one of the most popular character tropes in videogames after zombies and robots, but in all honesty, most of them suck at the one thing they are supposed to be good at. Ryu Hayabusa may strut around like a big ol' badass, but the trail of severed limbs and blood he leaves in his wake doesn't exactly scream "stealthy."
The world of Mark of the Ninja is cast almost entirely in shadow -- the darkness is your friend. Head-on confrontations are the last thing you should ever attempt, because exposure to light weakens your abilities. You have to run across rooftops and crawl through vents, destroying light sources if you feel that they'll give your location away.
The game presents all these functions that fans of other stealth games like Tenchu, Thief, or Metal Gear Solid would be intimately familiar with. When an enemy notices you, an alert noise will sound, then you must stay hidden until the timer runs down and the guards resume their normal duties. There are also various objects like vases and closets for you to hide behind or to stuff a corpse into to avoid detection.
When you toss your kunai at a gong, a metal grill, a light fixture, etc., it will trigger a sound that is represented visually by an expanding white circle. Any enemy within the sound's radius will be distracted, allowing you to sneak past. Conversely, sprinting and other actions can draw attention towards you. You must be aggressive yet discreet at all times.
Though direct combat is not ideal, you possess a limited set of attacks. Preferably, you'll want to sneak up behind an enemy for a swift kill. A button and a direction arrow will appear above enemies' head, and if you fail to execute the combo correctly, their deaths will be noisy and possibly alert nearby foes. On the other hand, sometimes you'll want to make a little noise. If you can kill an enemy in the presence of another enemy via something like an environmental kill, the second guy will freak out and start shooting wildly. You can then use his confusion to your advantage.
Mark of the Ninja values players' individual styles and won't demand them to play in a manner they are unaccustomed too. In other words, no Deus Ex: Human Revolution boss fights here. The "boss fights" are the higher profile targets that are protected by numerous guards or concealed deep within a building. The challenge comes in discovering the appropriate means in which to take the target out, not in whittling down a health bar or engaging in a flow-breaking brawl.
Klei is intelligently adding all these contextual clues and references to other stealth games to welcome genre fans and newcomers alike, all without making the controls excessively convoluted. You feel like a true ninja, wall-kicking up air vents and grappling across branches with a simple click of the shoulder trigger. A checkpoint is always close by, and the penalty for failure is never so great that you'll feel like you aren't making progress.
Mark of the Ninja comes out this summer for XBLA. It's got real ninjas. Ryu Hayabusa can suck it.