Fire from the Heavens
It looks like it's basically going to be about this guy:
Called the "Space Jockey" by fans, this long-dead creature appears early in the first film, and it's later obvious that he and his ship were earlier victims of the titular Alien, but he's never mentioned again. The fan discussion site has a lot of speculation about the storyline and the relationship between Space Jockey species, the Aliens, and humanity's origin, but clearly the trailers don't reveal as much as they seem to.
I do hope this movie isn't going to be wasted on just another trite "message" about technological hubris and "there are things man was not meant to know (or do)" clichés. That's been done to death a thousand times over -- since the Greek tale of Icarus, in fact. Science fiction, and the Alien saga especially, are capable of being so much more. I have a feeling the story will be more imaginative than most are expecting.