well there are only so many environments you can set a thing in if you want realism.
space: hyper future
space: alien (time setting varies, usually still hyper future)
modern times: civilized cities, usu. american
modern times: middle east or third world
war setting: usu. jungle, desert, or wartorn city
"old times": pre-WWII era, usu. a city like new york
"old times": wild west
medieval: sometimes fantasy (elves), sometimes realistic (no elves)
ancient: usu. egyptian or aztec civilization
modern: ancient ruins
modern/futuristic: snowy setting
futuristic: post-apocalypse
modern: post-apocalypse
Some games fall outside these settings, but the ones listed above are pretty much the tried-and-true.
Sure, you can make a game about a chinese diplomat visiting mars 5000 years ago, but it would probably be pretty boring (no air, no life, and how the fuck did he get there).
there are settings that haven't been touched on much, like caveman times, or the renaissance eras, or settings like spain, india, or northern europe.
but if you were in space, it sorta makes sense that you'd either be fighting aliens or robots. i mean you could fight other humans, but there's nothing new or different about that.
so i'm just trying to figure out here what could possibly be new, revolutionary, or creative, about a setting and an enemy today, as long as you're striving for realism. almost all of it's been done :/
dead space has very good mechanics and plays very well. and there actually is a very interesting aspect to the aliens that sets them apart from regular aliens. so it's a good game. it doesn't have to be about a turkey floating in a pile of jell-o during the revolutionary war, because unique doesn't always mean good :/