I like Alien, I like how it is such an animal demeanor, instead of being some intelligent life form spewed out by OJ-287 that then fell through a worm hole and discovered how to excel past the speed of light or something ridiculously impossible. Alien is one of the few extra terrestrial species that I can actually even half believe is realistic.
Why half? well there is because it has the demeanor of most life forms on earth, savage, angry, selfish, dominant and territorial, so right there it actually has the demeanor of a normal creature. Then there is the half the stops me from believing in it as much, It has acid for corrosive acid for blood, it has an inner mouth that has the speed and physical prowess to break through a human cranium in less than a second, it has babies that are spider like that can jump onto a creatures face and impregnate it so that an alien child will emerge in a small amount of time.
I still like Aliens more than the god awful predator movies, even predator as a movie character is just stupid. I would go on with why I don't like predator, but I don't want this to turn into a rant.