Alien terrified me. I've seen it *once* in my whole life (on video, so probably the screen cut rather than the director's cut, which I'd presumably get if I'd seen it on DVD) and it was daylight at the time that I watched it, and I still had nightmares several nights running. I have no capacity to evaluate it critically, because it scared me so badly. WHich presumably means that it did its job very effectively in terms of being a good horror/sci-fi movie.

Aliens, however, was still scary, but more manageably so. And I think your observation about the characters in the original being so darn ordinary is an excellent one, and may explain why Alien reduced me to a quivering wreck while Aliens merely frightened me. The marines with their pumped-up physiques and military jargon and barely-differentiated personalities weren't anything like the people I knew (even those Marines who got given some personality were still types rather than distinct and unique individuals). The crew members of the Nostromo could have been acquaintances of mine under different circumstances. So there was more of an identification. In Aliens the only characters I was able to identify with were Ripley and Newt; I didn't have an entire cast of regular people to agonize over.

But the ratcheting down of the tension meant i was better able to appreciate the less-scary stuff in Aliens. I enjoyed the movie a lot, and enjoyed Ripley's uber-maternal protectiveness (what is it with James Cameron and female characters who are total mama bears, anyway?) I thought it was a neat alternate focus, since we'd already done "focused on survival" for her in Alien. And the concept of the duelling Mothers was an interesting one. I was, however, annoyed by the final airlock scene, which I found tiresomely derivative. "Let's do almost exactly what Ridley Scott did in the first movie, only make it bigger and spend more money." is not an original idea.

Anyway, your analysis of the movies was really interesting. I still don't want to see Alien again, though. I'm a wimp.