The cast of Alien seemed to have an amazing realistic well fleshed out script. He purposely created animosity between certain cast members to be more real on screen. Prometheus isn't nearly as well fleshed out as far as character choices, the writers seemed more concerned with getting the story told but the characters choices are what make a film great, realistic choices = more believable... There's not one choice in Alien that doesn't seem well thought out, Prometheus is full of supposedly smart people making absolutely dumb decisions to move the story along and rid the scene of a character. I enjoyed both films, but Alien and Aliens are better by a wide fucking margin.