Alien is a story that began in the middle somewhat. So just like Star Wars, there is a story there that deserves to be told.
Now I felt that Star Wars took the wrong approach, specifically telling the story of characters from the original films, because we already knew what was going to end up happening to them.
I think Ridley will be smarter than that, though, and take the tack of new characters and whatnot, explaining how and why the events in the original trilogy came to pass, because there's still tons of unexplored ground there. Some questions are better left unanswered, but that doesn't mean I'm not dying to know the answers lol.