Aliens is a standalone masterpiece, while every other sequel is just blatant cash-grabbing.
Are you actually serious right now?
For me, the second installment is easily the worst one, right after the fourth, of course.
Like someone else already pointed out, it’s nothing more than typical action-movie filler!
The original Alien is definitely the peak. After that, you've got Fincher's Alien III—which honestly would have been a perfect way to wrap up the series—but then they completely botched it with the fourth one.
For some strange reason, I actually prefer Terminator 2: Judgment Day over the original.
I didn't enjoy Indiana Jones and the Last Crusade nearly as much as the other sequels.
And if I can add my two cents regarding The Exorcist I, II, and III...
After producing a true masterpiece like the first one, making such garbage sequels is practically a sin.