Three major observations from someone who has re-watched both Alien and Aliens quite a few times (and has seen the sequels once each... let's not talk about those haha).

First: given these movies are 30-40 years old, it is insane how well they have held up, effects included. The practical effects work on both these movies is stunning.

Second: these two movies work so well together in tandem, and make perfect sense from a plot perspective with the 50 year gap since the Alien ship was first discovered in between. With Alien, Ridley Scott gave us a really tight, terrifying, what the fuck is going style sci-fi horror movie that still works a treat to this day. With Aliens, James Cameron expanded the narrative scope of the universe in a really interesting way, and made an action thriller that in many ways is just as tense and terrifying as the first movie - turns out that whether you're an unarmed crew or a squad of marines, the aliens are going to go through you like butter regardless.

Third: even when judged just by on its own, individual merits, Aliens is excellent. 30 years later, and it remains one of the most spectacular action movies ever made. I've re-watched it very recently, and still had an absolute blast with it. The characters are fun as well, watching Ripley's character growth vs the first movie feels really genuine, and the pacing of the movie overall is flawless.

There's a reason it's so highly regard by so many - it's as close as we've ever gotten to a perfect sci-fi action thriller.