Alien: a perfect blend of sci-if, thriller, and horror. I could write an entire dissertation extolling the merits of this film, but suffice to say, it’s a contemporary masterpiece in every sense.
Aliens: while imitative of the original in some ways, this film at least shifts the genre from thriller to action, and in so doing establishes itself as unique. I also appreciate how this film creates a plausible reason for our protagonist to be thrust back into the action (something that plagues most sequels).

After that, it’s a four-way tie for last. Alien 3 was simply depressing, Alien Resurrection was a cartoon, and Prometheus and Covenant suffer from the same problems that plague the Star Wars prequels: aesthetically they do not match up with the preceding films, and narratively they’re unnecessary and uninteresting.

In many ways, it’s like watching a zombie flick; knowing how the infection got started isn’t nearly half as interesting as seeing how people cope with the outbreak. That’s pretty much the case with the Alien prequels — I don’t really need or even want to know how the xenomorphs came into existence, I just want to see how people deal with them.