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.