The Alien in Alien was a humanoid bug with a lil' mouth in his mouth that came from a facehugger having it's way with a crew member that came upon it from an egg. The guy goes around causing a ruckus by killing/raping/eating it's prey and occasionally (as the deleted scenes shows), makes some love goo to put people in to incubate them. It dies when a flamethrowin' lady goes around and cleans up it's mess, but wait, it's not dead! Surprise! It's really on board with her until she sends it off floating into deep space.
The Aliens in Aliens were humanoid bugs with lil' mouths inside their mouths that came from a facehugger having it's way with a colony of people that came upon eggs. The guys go around causing a ruckus by killing/raping/eating their prey and occasionally make love goo to put people in to incubate them. They die when a flamethrowin' lady goes around and cleans up their mess, but wait, there's a Queen, a big momma just like Ripley. Surprise! She killed it! Not! It's really on board with her until she sends it off floating into deep space.
Eggs, facehuggers, lil' mouths within mouths. Whatever. Same humanoid bug (or sexually organic, giger weird ****). Difference is, in film one, there's one and in film two, there's a lot. If I'm a monster/animal/whatever, I'm going to act differently when I'm on my own in a small, claustrophobic ship than I would if I'm hanging out with all my bros in an open environment taking on the military. People can act "buggy" and hive minded too.
Seems to me like people have this weird idolization or primadonna thing with the first Alien or Terminator. They're put on a pedestal and it's like somehow, there can't be more of them, and if there are, they're not as bad ass or as cool as the first. I don't get it, it's silly when we're dealing with creatures that can be remade, either through birth, or in the case of the Terminator, assembly. We never saw the Alien do anything extraordinary except grow from a phallic looking alien that burst out of a man's chest, which turned into an adult sized space monster that went around killing people (assuming it has the intention of surviving and procreating like any living being). Yes, it was special because it was the first, but there were also hundreds/thousands of other eggs there, all with facehuggers. The sequel deals with the "what if" of that and we have a little colony of people that helped give birth to more monsters. It's not about the "mysterious" Alien, but about Ripley going back and facing those demons again (just like T2 isn't about the Terminator or how "bad ass" he is going in and killing a lot of cops, it's about Sarah Connor overcoming her nightmare and making peace with her prejudices).