It'd been about 20 years since I last saw Alien, and then it was only because a roommate demanded it of me. I've never gone further into the franchise.
We've been trained to go into every movie as if it's an amusement park. There was a time (and Alien is a prime example) when movies were approached as art exhibits. Yes, Alien has moments of horror. But it's not primarily a horror film designed to carry us on visceral reactions. Instead, it's a finely tuned suspense movie.
In every frame there's something to consider. It might be the characters, how their unique motivations and personalities draw different things from the others. It might be the texture of the ship, not polished like the USS Enterprise or an Imperial Destroyer, but wet and dirty. It might be space itself, which is vast, unknowable, and filled with unspeakable terrors.
H.P. Lovecraft knew a thing or two about unspeakable terrors. He wrote, "Atmosphere, not action, is the great desideratum of weird fiction. Indeed, all that a wonder story can ever be is a vivid picture of a certain type of human mood."
It's not that you need to be "media literate" to appreciate Alien. The media literate person will look at the opening of the movie and note how the camera floats through the empty ship while the crew is asleep to give us, the viewers, the sense of intruding where we don't belong. If that's your thing, I'm right there with you. Most people don't want to be media literate, and that's a good thing.
In order to appreciate Alien, all you need to do is allow yourself to slip into the atmosphere, the mood, it creates.