It still holds up!
It's a film I've revisited many times since I first saw it in the early 1980s. At first I just enjoyed the horror and suspense aspects of the film, but subsequent viewings have made me appreciate how groundbreaking it was to have a female lead, the gender-reversing shock of seeing a man 'raped' by an alien, HR Giger's masterful bio-mechanical set and creature design and the deliberate but operatic pacing of the film.
Perhaps the thing that has kept the film in the public consciousness and made it a cut above the average 'slasher' film is the fact that there are some intriguing questions set up that are left unanswered. Who was The Space Jockey piloting the ship which carried the alien cargo? What is the faceless Weyland-Yutani corporation? What is the extent of their knowledge of the Xenomorph? Is it a bio-weapon? The sequels to Alien wisely stayed away from answering most of these questions. I think this is largely because the fans wouldn't want to see these ideas tackled by anyone else but Ridley Scott (or perhaps James Cameron).
Prequels, reboots and sequels to beloved genre-films are a dime a dozen these days and I'm generally not a fan. The Star Wars prequels are the perfect example of why they don't work and I can explain why in one sentence - No amount of money or CGI wizardry can compete with a 10 year-old's imagination when it comes to envisioning 'The Clone Wars'. Alec Guinness' passing mention of it at the beginning of Star Wars was enough. Save yourself the time and money, Hollywood. At best prequels seem to disappoint and at worst they damage your opinion of the existing films (and your childhood memories)
If you don't believe me, then maybe Simon Pegg can convince you: