Disturbing, Oppressive, Horrific. In other words, everything I want from Horror!

Rating: 9/10 (19 November 2019)

Made in the late '70s, Alien became the prototype for genre films going forward. Before they relied on quick-cuts, jump-scares, and digital effects to create our "horror", filmmakers instead used pacing, theme, and a combination of attacks on our senses to keep us constantly dreading what may be around that next corner.
The slower pacing, accentuated by longer takes and establishing shots, allowed the dread to build Because of this, the payoff was very gratifying. Some of this came from technical limitations. For example, they really couldn't show the "alien" in its entirety as it moved around simply because it would've looked a bit hokey. Instead, as with Jaws before it, Alien shows us glimpses, suggestions, reactions, and aftermath. When we do finally see the alien in its full glory, it is indeed glorious.
The filmmakers used the oppressively dark, wet, and mechanical environments to hide the threat in plain sight, forcing the audience to feel a little bit of the helplessness felt by the characters.
The director also tricked the actors into visceral, horrified reactions through sneaky and ambiguous direction coupled with extreme practical effects.
The idea behind this movie could've been done in any isolated, close-quarters environment. The fact that it was an alien on a spaceship simply added to the overall feel and impact of the movie; however, it would've been nearly as effective if set in, say, an Antarctic outpost, or in a submarine, or in an abandoned research lab. Because of this, it sparked a rash of imitators in those exact scenarios (and more).
Alien is a classic horror film. An icon. That said, it just may fail to have the same impact on modern audiences. The slower pacing, deliberate story beats, low-tech effects, and dialogue-heavy scenes would likely be seen as "boring", and might risk losing a less mature audience before the big fun even begins. This is a shame, but I doubt many younger horror fans would get as much out of this movie people did when it was first released.
That said, if you want to see where this style of horror reached its zenith, look no further than the xenomorphic sci-fi body-horror of Alien.