Alien was made in an era which, in many ways, I feel was the age when movie making reached its zenith. Not just because of the art itself, but because of the world in which they were made.
I mean, the late Seventies. The tail end of the hippie age, right before the great Beast rose in the White House - the children of the flower age, now fully grown and developed, at the height of their ability. What movies were made in those five years?
A handful of them: Rocky, Taxi Driver, Carrie, The Omen, Network, Logan's Run, All the president's men, Marathon Man, Star Wars (back before it was called 'A New Hope'), Close Encounters of the Third Kind, Smokey and the Bandit, Annie Hall, Eraserhead, Saturday Night Fever, The Hills Have Eyes, Grease, Halloween, The Deer Hunter, Superman, Midnight Express, Invasion of the Body Snatchers (the best version), Dawn of the Dead (mother of all zombie flicks), Watership Down, The Lord of the Rings (the animated one), The Boys from Brazil, Sergeant Pepper's Lonely Hearts Club Band, Mad frickin' Max, Apocalypse Now, The Warriors, Caligula, Kramer vs. Kramer, Life of Brian, Star Trek: the Motion Picture, the Amityville Horror and The Black Hole (Thanks, IMDb).
Compare it to what's being groaned out by Hollywood today. It's no comparing.