I wasn't disappointed by it (I've seen it twice now because I wanted to see it again after the initial viewing and realised it was a different thing than I had expected) but I think I had the wrong set of expectations about it before I went in, as I had been trying to avoid a lot of the trailers etc.
I like the first two thirds of the film, but I feel that the final act lets it down because (without giving away spoilers) the whole thing seems predicated on there being more films to continue the story that has been set up in 'Prometheus'
I found the film stayed in my mind after watching it and that I was interested in thinking about what (if anything) it might mean and I would have to say that it's really a film that wants to be a 1970s 'think piece' of science fiction for the first two thirds and then decides to be a normal contemporary Hollywood action spectacle in the final third and they don't mesh well. And I am left wondering if the ideas themselves are on a road to somewhere or a road to nowhere. Only sequels will tell that, though.
I liked it. I liked it better the second time around without the weight of thinking that it would be like 'Alien'
, which I can safely say it is not (and as I think more general reviews are starting to come out that should be less of a big secret by now). On the plus side, I think it's visually beautiful in all areas as well.