It's very rare when the Academy Awards reward a performance in an action film. Then again, it's all too rare when a performance dares to stand out in an action film, and especially from a heroine. No, if you want a Best Actress nomination, you pretty much have to smash the loudest plate or have the most sickly terminal illness.
That is, unless you're Sigourney Weaver in Aliens, and you already rose to the occasion as the lone survivor of the commercial starship Nostromo. Now you wield maternal instincts as fiercely as you do a flamethrower when stranded on a planet full of nasty extraterrestrials just like the one that took out your previous crew, and instead of oozing cool like so many Marines around you, you sweat and worry and scream, which makes us care all the more when the Marines start getting picked off one by one.
Let me repeat that: she makes us care in what is ostensibly a two-hour-plus monster movie.
Of course, it helps that she already made us care with Alien. As Lt. Ellen Ripley, Weaver stood as much of a chance of survival as anyone else in the cast -- after all, she had had a bit part in Annie Hall before that and not much else, and with no one or two individuals standing out on the poster or in the first act, her character was just as likely to make it out alive as Tom Skerritt's or Yaphet Kotto's was (but not Veronica Cartwright's -- she was just too damn whiny to stick around for long). We can already suppose that she's a blue-collar type, not tied down by family OR in it for the long haul in order to support her family, so in a sense, she's already been fending for herself since before the acid blood starts to hit the fan.
Lo and behold, she does survive, with both her and the cat left adrift in space. That's where James Cameron's Aliens picks up, with her awaking after fifty-seven years in hypersleep. Anything she knew back home on Earth? Gone by now. Cameron's special edition would confirm that she had a daughter, one who died in that span of time and thus give further cause for Ripley to take care of the newly orphaned "Newt" (Carrie Henn) once she returns to the planet from the first film with Marines in tow. Initially, she was just going back to confirm that she wasn't crazy, or maybe prove that she was, and to do anything and everything she could to keep those creatures at bay.
Once she accepts the mission, we accept that Ripley has the steely resolve to see it through. If Aliens somehow existed without Alien already establishing this (or, more likely, if someone was seeing Aliens without having seen Alien), the inclusion of her late daughter makes her motives more sound. After all, there are families on that planet now. Even if nothing's left for Ripley, don't they deserve a warning, if not a rescue? And hey, if she quell her own traumatic experience in the process, that helps too.
And so she goes, and she grows. She adapts as much as her enemies do, saving the Marines when they can't save themselves, learning how to take them out with the best of them and then fighting alongside the rest of 'em. She has a girl to protect now. She has friends to save now. She's given renewed purpose by way of these beasts, so by the time she's staring down the Queen Alien, we understand her cause for terror but also buy into her newfound resolve. And by the time she's strapped into a power-loader and slapping said Queen around, we didn't clap and cheer because she said a cool line and obviously fighting the villain. No, we're seeing Ripley assert herself, in ways that she couldn't in the first film and has to by the second.
Yes, Weaver would go on to earn more Academy Award nominations for more conventional work, but it's this performance that has defined her cultural influence. Ripley is a woman who, after spending nearly sixty years fighting aliens (and with whom we as viewers have spent a good four hours with), has gone from being (rightfully) scared in her skivvies to becoming one bad-ass mama with nerves of steel and a heart of gold, and Weaver is an actress who, at a time when female roles in genre fare were skimpy beyond stripping down and screaming, took things to the next level.
She made us care, and that is the real reason why this one moment turned out be so damn cool...