Well, that could be done too, but this way player will be able to kick monsters ass, so there should be a bunch of monsters, that's what I don't like to do.
So make it so killing monsters isn't just a matter of pointing at them and clicking. Like Dead Space for example invented the whole strategic dismemberment thing, so suddenly one bad guy is a more serious problem since you can't just shoot at it, you have to aim at each of its limbs and knock them out one at a time. It's more complicated and it's new and fresh, and therefore it is fun.
And I'm not saying you should copy *that* design directly... but you should try being more inventive with your gameplay first and foremost before you put effort into settling on an art style.
Bioshock went through a ton of revisions in its visual design before they settled on the underwater city theme. Originally it was going to take place in a nazi bunker. The one thing that stayed constant through the game's development though was the Splicer -> Little Sister -> Big Daddy thing. They took that design and made it a huge part of the game from the beginning. So you need to think of interesting concepts like that before you try to imagine what kind of weird settings your game should take place in, because it's not the art style that makes the game, but the game design.
