The creature in Alien is a humanoid-looking individual that takes out the crew of the Nostromo one by one like Bruce Willis in space, but it also uses them to procreate.
In Aliens we have a Hive. A Queen that lays eggs and an army of drones that rush and kill the guys with automatic weapons.
In the end, both can't get the job done - and it's just a matter of taste what you prefer.
I like the concept of the more intelligent/self-preservative individual stalker from Alien more and hence feel like the "strength by numbers" approach (as good as Cameron's film is) was as necessary as an army of Hannibal Lecters.
Plus turning one victim into an egg of yours to impregnate another (victim) is so much more alien than a Queen laying eggs.
I understand this point of view, I just never saw the films as distinct as this. Tonally yes, but when I saw Aliens it felt very much like a natural expansion of the first. They're studies of the creature as much as a study of our own fears brought out by it.
The approaches of both films do work, do both get the job done, and both are inherently linked as the quote from Dan O'Bannon on the previous page makes clear; he felt the insect life-cycle was crucial to Alien and even profoundly important from a psychological point of view. The insect thing was always there and key to it.
We see the egg chamber in Alien, this isn't just an individual stalker monster from outer space. We have loads of films like that. It's a species. Alien is unique in that the monster of this horror film has a detailed life-cycle for once; it's a force of nature and much more believable and terrifying because of that. I think that's part of why it has endured so much.
We are meant to try and understand it, not just view it as mysterious and alien. Dan O'Bannon said he didn't want to dumb the biology of the creature down but detail it because nature is scary and realising that is where the fear comes from. The xenomorph takes on humanoid qualities as a result of the parasitic nature of our encounter with it, which taps into the human conditions of rape, pregnancy and childbirth. It's about how its life-cycle is at odds with our own. All Aliens did was show us more of that, and introduce motherhood as another parallel for when these normally distinct life-cycles, human and insect, collide.
How you encounter the creature also shapes how you see it, as in nature. In the same way as one spider being loose in your house can be just as scary as your house being overrun by them. It's a different type of fear, which provokes a different type of response. We naturally attribute significance and qualities to an individual rather than a group because our focus is on an a sole individual which magnifies it. The Queen in Aliens is quite literally that magnified individual, just now given a reason for being so.
Neither approach undermines the other in the potential of the creature to elicit fear in my opinion, both Alien and Aliens are about exploring the cycle of life and the horror of nature from our human understanding of it.