They've aged very well (other than the suspiciously low tech computers). Aliens still is still the boss alien-fighting movie.
I reckon a good test of the longevity of a film is the quote quotient.
Aliens scarcely has 5min without some fantastic lines, hearing them instantly flashes back to the scene.
".. nuke the site from orbit, it's the only way to be sure"
"Get away from her, you bitch"
"She doesn't have any bad dreams because she's just a doll."