Let there be Prometheus
I thought the movie was good, great even if you haven't watched any of the trailers. Michael Fassbender played a perfect evil android, from the stiff posture to the robotic reactions to things around him. I wasn't exactly sold on Noomi's character but she did a great job with it anyway. I don't normally like Charlize but she did pretty damn good, too. For a while, I was curious if she was a droid, too.
The movie provided some possible answers to other questions. One that we now know for certain is that the company knew exactly what was going on on LV-426 once the language in the SOS was deciphered. Second, we know that the Engineer who died on that ship made a mistake, but was clearly headed for some system where they intended to deploy the aliens (while AVP has provided some great comics and novels, I find this a more interesting premise than a yautja male initiation rite). Third, the aliens were definitely biological weapons as opposed to a naturally evolved species.
After that, the movie lets you make up your mind on a few things. Captain Janek notes that the Engineers are smart enough to build their biological weapons someplace other than their backyard. They are also smart enough to give their creations a map to the bio depots instead of their homeworld - would you want your creations showing up at your doorstep with who knows what microbes and military weapons? Now, Shaw is leaving the depot to go back to their homeworld. Flying a ship that's likely loaded down with biological weapons. There might be a very good reason that the Engineers don't have any future involvement with humankind.
Another thing is that Janek notes this planet is a "lab". Earth is another "lab". Shaw isn't going to get the answer she wants when she heads back to their homeworld, assuming she gets an answer at all. She's probably going to hear that humanity didn't fuck up, they were just another petri dish and they were going to see what happens when two dishes combine. That answers the biggest question: Why? Because they could. Just like us, their descendants.
The only real question I have that I couldn't intuit an answer for is what happened in the opening scene. It almost looks like that Engineer was exiled, or left behind, and decided to commit suicide. Not sure why that would be worth the scene, though, so I think there's another reason it was there.