The premise is only part of what makes a film work or not work. Ridley Scott mentions a few times during his commentary for "Alien" that the premise for Alien was very simple and in fact had been done before but what made it unique was in HOW that premise was presented along with of course HR Giger's genius behind the xenomorph and the derelict ship design. Naturally, film is a visual medium and "Alien" had a very unique and striking visual style for the time.
There is no denying that Alien captured lightning in a bottle. Cast , script, effects, music.
But as good as that can be, you can repackage it and keep selling it just so many times. Can there be another Alien? What will it take?
So it might not have been original, but now it is on a class on it's own.
I have said this before, it took adding a tornado to make killer shark movies relevant again (even as the quality was greatly decreased). Same with alien monsters. We need something that changes it more than the setting.
