Here's my entry so far, got a little more to go on this before it's fully done, but I can at least explain what I'm thinking.
So in my ninja game, "A Business Time
To Kill" the entire thing takes place in a giant office building type place, a la high rise building style.
So, in it you can play either the bad guys (shown above) in a splinter cell style game, and your goal is to off as many office employees without getting caught. In this side of things, you're invincible, because let's face it, ninjas are just that. However, getting caught can cause various things, such as calling up the Business Ninja, who is the protagonist of the good side. If you're caught by him, he will almost definitely kill you, a risk you take messing with a master ninja. At some point you could become so bad you could kill him,but needless to say I haven't gotten that far into the thought process.
The UI would act somewhat like a point-and-click interface, in that certain areas will have special events you can perform, such as taking out the lights in that mockup above. Obv. the more stealthy you are the better the kill (which reminds me, I should add a point ticker to that screen)
In any case, more on the other side when/if I make another mockup. Enjoy this for now.