SC had a TPS a la gears of wars about ghosts. not a FPS. unless gears is a fps.

and cm'on, admit they are REALLY similar.

zergs and floods : gross alien race that consumes living beings, incorportating your own units against you (infested terrans for zergs, flood brute/jackal/marine/whatever), hellbent on conquering the universe, led by a giant brain (overmind for zergs, gravemind for floods), enemies of every other factions. the only real aesthetic difference is that one looks more insectoid, and the other more like it's a virus.

covies and protoss are both techologically advanced races, enemies of humanity, with religious aspects in their society. they fight both floods/zergs and humans.

terrans and unsc ... well... humans, rely on technology, blabla. you know, us.

now if you go in details, there is nothing similar. but if you indeed go into details about EVERYTHING EVERYWHERE, then art theft/copying/stealing doesn't exist, because you HAVE to change some stuff (like name, storyline) or the game/movie/whatever would not even get funds in the first place.