Someone said :
But Prometheus is not a prequel.
It started off that way but ended up being changed into a movie in it's own right.
Why do people still think it's part of the Alien movies?
It occurs before the movie Alien, on the same planet where the 'Distress signal' is picked up, in the same alien space ship with the same 'space jockey' (now called Engineers'. It has the alien queen carved on the wall.
Its not the direct prequel they had planned on making, but it is by definition a prequel, in the same way the hobit is a prequel to Lord of the Rings. And with the second movie planned it looks as if there is going to be an even more direct set up for a seamless run into Alien.
Still a shite movie.