[Ripley’s] final act is a sad - albeit selfless - end and the one time in the three films she’s ever, truly been in control of her own fate. She takes back control over her life by ending it in defiance of the Xenomorphs and the corporation that have combined and conspired to haunt her for unknowable years now; and the relief on her face is the last image we have of her life, her journey, and her fate.
I think Spytap’s right. The much-derided “Alien 3” may be flawed, but it contained elements that were necessary to the proper completion of the story. I always felt that it had a kind of theatrical feel about it, like a play from some particularly gloomy culture, say Swedish or Russian. Maybe the whole trilogy (let’s ignore the pretty but vapid “Alien Resurrection”) should be retitled “The Tragedy of Ellen Ripley”.
Tragedy requires ἁμαρτία, but Ripley’s fatal flaw doesn’t seem to be a defect of character, but simply that she is always in the wrong place at the wrong time. She does share one characteristic with another famously tragic character, though. Like Cassandra, Ripley is always right, and her warnings are always ignored by everyone around her (at least until it’s too late).
The most enduring science-fiction films do seem to play out as tragedies. In “Blade Runner” (aka “The Tragedy of Roy Batty”, aka “The Passion of the Replicant”), the characters all share the common flaw of mortality. And “Star Wars” (“The Tragedy of Anakin Skywalker”) should be a classic tragedy about a good man brought down by hubris. At least that’s what Lucas was apparently aiming for, although he manages to make such a dog’s breakfast of it that at times it’s closer to farce and the tragic intensity ends up being entirely squandered.