Finally watched this over the weekend. I can't say that I enjoyed it; I think the word that comes to mind is "bland".
What I would have really liked to see was an exploration of why the Engineers would feel as they did about humanity. Personally, I think it was a play on the definition of "alien". In the mind of the Engineers, humanity were the xenomorphs; freak mutations who are smaller in stature than the Engineers but dangerous in their own right.
Prometheus was a monster movie just like the original Alien. However, the humans were the monsters while the Engineer was the lone surviving hero trying to destroy the human infestation before it moved on to his home planet.