My remarks from the other Alien
I really hope Scott doesn't explain the alien ship or the Space Jockey. I'm all for expanding universes, but some things - such as Yoda's origins or how Superman shaves - are best left to the imagination. Also, I agree with Weaver's recent comments that trying to make a "new Ripley" is kind of lame - I love the Ripley character, of course, but why not have a different, even male protagonist, next time?
I'd most like to see a post-Aliens
movie that ignores all but the first two movies and shows us a totally different aspect of the universe, with a similar look and feel, but a different kind of story, maybe well without the Aliens at all. Of course, that does pretty well describe Avatar
... (the tech and corporations parts, that is.)