-Bloo-,
Yautja,
15 years ago
But the Alien was never fully portrayed as an immortal shadow thing. The only reason it was never killed was because the crew was unarmed, ill-prepared and just normal people. The Warriors in Aliens were so easily killed because they were facing trained and armed marines briefed for the mission. Contrary to popular fan belief, they were, in fact, very much the same creatures you saw in Alien.
Aliens was basically just a huge What if?..., the 'What if' question being, "What if the guys in Alien were armed?" Later on in the movie it demonstrated how you take that question and make it interesting: Hey, let's add a Queen.