yep, it truly is a classic.

As for getting another film like it, obviously it’s really a sub-genre of its own, so anything too close is just a copy/clone.

But as for what generally makes it a classic, I’d venture (off of the top of my head) that what Ridley Scott himself says is pretty on the mark: B grade horror done like A grade film. More generally, it’s the rendering of something that’s remained “under-produced” and exclusive to a sub-culture into a higher-production and dramatically serious and high-caliber form.

If that’s part of it, then it’s interesting to ask what other films have done that. Suggestions, off the top of my head:

• The Matrix comes immediately to mind (anime, cyberpunk, hong-kong martial arts films done as a Hollywood blockbuster).
• 2001 A Space Odyssey probably counts (I’m not really sure how Sci-Fi was viewed before 1968).
• Lord of the Rings (high fantasy, though I wonder if Star Wars is the real predecessor of this?)
• Comic book movies probably count to some extent here (Burton’s Batman, Nolan’s Batman and the first Iron Man?), but I’m loathe to include them because I think they’re all kinda derivative of the above, with Burton’s Batman probably being an exception but also not so much of a perfection of content and form that Alien and the above were.
• Pulp Fiction?