What is the Alien Universe?
Is it like a B movie horror franchise? (Like "Halloween" which has 11 slasher films or "Friday the 13th" which as 12? Only set in space?)
Some want it to be this way.
To me Alien was different. It was first science fiction then horror.
"Alien" laid the ground work & "Aliens" expanded on it using ideas from Hill & Giler.
But as science fiction the franchise stagnated with "Alien 3" & "Resurrection". While entertaining, 3 & 4 were mostly focused on Ripley as a loner which is what Sigourney wanted.
The development of what the xenomorphs were was limited in 3 & 4. They could walk like a dog. They could swim. Not much there. Nothing about the Space Jockeys.
In space travel science fiction franchises, information about important alien species is expanded over time.
The Alien prequels did this with the Space Jockeys and xenomorphs as well as adding other related creatures.
Space travel science fiction adds new, unusual planets which were in the prequels.
As science fiction "Prometheus" and "Covenant" added a lot to the Alien Universe.
And I enjoyed that.