The crew SHOULD be like HOLY CRAP there is a civilization on this world. What happened to them, how in the world did you survive, etc. etc. David giving second hand explanations for why some aspects are the way that they are.
Well, at that point in the movie they don't feel safe, they're in a state of shock, most of them have lost the partner they gave up life on Earth to go live with, and they're following someone they know they have no reason to trust. If they were landing there for a scientific mission with no immediate danger surrounding them like in Prometheus then yes, I'd be annoyed that they're not trying to figure out more about this civilisation. In context, it's sort of ok.
As for the audience, there is plenty that is not stated but shown ( most of it already leaked through trailers ), so it's not like there hasn't been any effort put into it. In fact, by frame freezing when the movie comes out on dvd/blu-ray, during the scenes taking place in David's lab, I wouldn't be surprised if we ended up with a lot more details about the Engineers. I remember a moment with a big diagram of an Engineer in full sight.