Still be interesting to see if the next 2 films go back to the reason the Engineers wished to wipe out humanity. All this talk of space Jesus (which even though I'm not religious, I certainly wouldn't want to see) and the rise of the Roman Empire. But I also remember Lindelof and Spaihts mentioning the possibility that our creation was just an experiment and that the earth is little more than a petri dish to the Engineers; an idea I personally feel ties in much better with the whole Lovecraftian feel, that most fans seem to want with an Alien origin story.
With that in mind, I'm really hoping the Xeno-like mural on the wall in the ampule room, is more than just an Easter egg; included for no other reason, than it being the only piece of artwork Giger contributed to Prometheus.
My preferred direction by the end of these prequels, would be to find out that the creature in mural was central to the plot. And what the Engineers were really doing on LV-223, is trying to resurrect that creature, an ancient god like being, long extinct, who's blood is the basis of the mutagen they use in their sacrificial rituals, to seed other worlds. They knew the creature was parasitic in nature and would require living hosts, so just arbitrarily selected the human population on earth, for the honour of birthing their deity. But the Engineers messed up. Rather than recreating the creature from the mural, the black goo creates abominations of it instead; which David later perfects through his experiments on Paradise.