Why Bother? Prometheus, with spoilers
These are things for writers to consider.
Plot and theme hinged on the motivations of the characters, and were, like the characterisations, a bit weak. This wasn't the fault of the actors. Charlize Theron did a particularly good job of portraying Vickers in a way that warranted the captain's question, "are you a robot?"
The android, David, was interesting, too, but he could have been different in ways that worked better in the Alien universe and still been good.
An example of what's wrong with the film is the way Vickers died. It was as if she was being punished for something, but what? She looked out for herself in a way that was sensible if selfish - she wasn't sharing with the others - but not evil. So why the punishment?
Vickers life pod was another example of things wrong in the film. When the main protagonist, Elizabeth Shaw, runs into Vickers quarters/life pod seeking medical aid so that she can abort the alien inside her, she finds that the medical unit is only programmed for men.
Vickers must really have been hiding something in that skin tight suit she wore.
And why send a medical unit into space with a mixed crew and only program it for men anyway?
Shaw has her hi-tech operation which ends with her stomach being stapled back together in a high-speed, high-tech fashion that makes the staples themselves look very low-tech. Shaw then jumps up and runs for her life, sometimes leaping emerging chasms, and then running some more. She's just had a ceasar and she's got staples, but she runs and actually get well on the run. All this while presumably greif stricken over the death of the love her life.
Shaw is the least well worked out character in the story, but she's the main protagonist. She's the one who transmits the story and then goes off into the future searching for her creator, although she is a Christian and presumably knows who her creator is and ... This is another one of those points where the story makes no sense. It's another one of those points of missed opportunity. Shaw is a Christian. We are told, but never shown, that she is strong in her faith. It would have been more interesting to show her being tested in her faith the very moment she came to believe that aliens had something to do with the genesis of mankind. In the film she is just someone who believes stuff, whatever that stuff is she believes it. She could just as easily have believed in magic mushrooms. Her scientific background is similarly vague. Whatever the plot needs her to know at that moment, that's what she knows. This gives her no particular style of analysis and weakens the film by giving it no particular train of thought, or theme.
Themewise, there is a vague notion of genesis and the story of Cain and Abel, which isn't at all played out in Prometheus. Vickers is largely rejected by her father, who favours David the android. David is a robot and should have no feelings but is sensitive on this topic. For a moment (he's beautifully played by Michael Fassbender) he believes he is the accepted child of the giants, but he's quickly torn from that notion.
All in all, a lot of money was spent on this film, but if a bit more of that budget had been spent on perfecting the script we could have a much happier audience today.
First up, the characters were interesting in gimmicky ways that would have been far more interesting if more thought had been spent on them, and possibly if there had been fewer of them. Some films with ensemble casts are wonderful, they give you each characters story in a way that's unhurried and which makes sense to the whole of the film. This is not the case in Prometheus. Should there have been fewer characters so that proper time could have been spent on the remainder? Could there have been less time on special effects and running around so that there was more time to spend with the characters? If it's the special effects that are important to you, and especially if you are thinking about the possibilities of 3D and computer games, do you find a story instead that cuts back on the number of characters and makes one of them the environment?
It's easier to criticise Prometheus than it is to be someone who can come up with an original story in the first place. On the other hand, there are plenty of writers in the world who probably could have done it. How would you have done it? Myself, I think I would have looked at the biotech designs Giger gave Alien, and meditated my way into a story from there. It might have taken a while, though. I might have used the idea of the android, but made it different from the 'evil' android in Alien, possibly made it not evil at all so that Ash's betrayal of his human comrades in Alien might seem all the worse when viewed again.
Actually, I've always felt that the truly evil being in Alien was The Company, who put Ash there and wanted the alien brought back to them.
In short, and in conclusion, I think Prometheus was bad in very simple ways that, like the Star Wars prequels, make is easy and useful for us to consider how it might have been done better.