The Prometheus starship has been funded by the Weyland corporation to visit a distant star system, apparent home to 'The Engineers' who originally seeded human life on Earth.
Naturally what they find on alien world LV-223 is something rather different: a mission to revisit Earth with a contrary objective in mind. Wikipedia entry here.
Let me first agree with the critics: 3D on a large screen rewards the astonishingly immersive vistas Ridley Scott has conjured up. This feast for the eyes is not wholly matched by either plot or underlying concepts.
Science-Fiction films, once you strip the surface CGI away, live or die by their sense of wonder: think of the enduring appeal of The Matrix. In this sense there are few, if any ideas in Prometheus which depart from the mundane. This leave only plot to carry us through.
Elizabeth Shaw (played by Noomi Rapace)Under the SF hood, this is the story of an idealistic woman Elizabeth Shaw (played by Noomi Rapace) engaged in a hunt for her tribal origins. Her 'revered ancestors' turn out to be a hideous foe. By some miracle, after terrible losses, she survives and continues to search for answers (in the sequel). It's a familiar archetype and by that very fact engrossing if done well. And Scott has told a good story here, which amply repays the admission fee and two hours of your time.
But it could have been a lot more if they had built the script around a deeper, more creative and more original premise.