No surprise for me, Alien and Aliens are great movies. I find it amazing that "lighting in a bottle" struck twice for this franchise and I doubt it'll happen again.
That said, of the two films, Aliens has a much broader appeal to general audiences. I find it hard to get people to who haven't seen Alien to actually appreciate its slow & quiet style. The effects in both flicks have aged some-what as well, even in the nineties my friends always tried to rag on the films by pointing out the men in suits.