Aliens was a fun action movie but it was pretty bland besides that.
Alien was a much better film, with a much more likable cast.
But the real problem with Aliens, and why Alien is superior, is the alien itself/themselves.
I dislike how the Alien's intelligence and threat level is directly proportional to how many there are. A single Alien like in the first movie, or even like in *shudders* Aliens 3 is a forced to be reckoned with and could easily outsmart the buffoons in Aliens who are about as 80s Action Hero as you can get. We're talking Arnold in Predator-levels of competence where he says "Knock knock!" after opening a door on an enemy in his raid on their camp.
Yet you have a bunch of them together and suddenly they adopt Zapp Brannigan's intelligence and strategy
Why did they just keep rushing the sentry guns until the sentry guns were out of bullets?
That single alien in Alien was a greater threat than the whole damn hive in Aliens.