An amazing idea that is ruined pretty quickly

Rating: 5/10 (20 October 2012)

The opening sequence was the best part of the film, the idea is that on a barren world capable of sustaining life, one of these "engineers" sacrifices himself to start the evolutionary process.
Beautiful.
BUT the question that keeps popping up in the movie is "Why"?
Why would it be necessary to do so, I mean they have interstellar travel capability, why not just mix up some "evolutionary soup" and drop it in the ocean, why sacrifice someone?
************************Spoiler alert*****************
If the planet was supposed to be earth then why did we evolve into a genetically identical species after 3 billion years?
Even if it wasn't Earth, then why would they visit us several times and leave us a map of how to find them, when the map only points us to an outpost world where they park ships?
Why were the engineers fleeing through their ship into a room full of hyper-evolutionary bio-juice? What was chasing them and what happened to it?
Why does the last of these engineers, asleep for 2000 years, want to kill everyone the moment he wakes up? Why would he want to wipe out our world? I know I can be grumpy when I wake but that's a bit extreme.
Some thoughts occurred to me that maybe these bio-warfare engineers were not the same as those seen in the beginning sequence, but that would mean more than one species of genetically identical sentient beings arose on different worlds in roughly the same time frame which would take us into whole new realms of improbability. If they were the same engineers as those in the beginning and that was Earth, then they haven't evolved much at all in 3 billion years. Too many questions, no where near enough answers.
And that's not even going into the ridiculousness of the crew and the Prometheus.
Between archaeologists who poke everything and contaminate locations that have been sealed for 20 centuries, space suits with GLASS bubble helmets, hyper advanced auto-docs that can't handle the difference between male and female anatomy, reanimating alien heads that have been dead for 2000 years, frail old men who survive hibernation which we see makes healthy people weak and sick, and scientists who don't know the difference between carbon dioxide (CO2, not deadly at 3% purity) and carbon monoxide (CO, deadly at 1.2% purity)
I have to say the movie fails on almost all levels of sense-making.
I gave it 5 stars because of two things, the opening and the beautiful imagery of the film.