Saw it. And ugh. To all those who reviewed it in the thread, you were far too gentle. It's a let-down unfortunately.
Here are my spoiler-free two cents. I find that Prometheus's trailers were a big detriment to my experience; they gave away far too much, both visually and plot-wise. This movie needed a more conservative ad campaign. I also felt like some lines were added, for the purpose of being in the trailer; most of the advertised lines (eg. "Big things have small beginnings.") seem rather abrupt in the actual movie.
Prometheus has some positives. Like everyone has said, the visuals are great. I will not dispute that. I thought the effects were spot-on: perfect combination of CGI and practical effects. Scott sure knows how to make sci-fi look right and realistic. As many reviews have stated, the acting, in so far as the leads, (Fassbender and Rapace), was great. They had thoroughly interesting characters.
Now, the negatives: Though the acting of the leads were good, I couldn't determine exactly whose story this was supposed to be; in other words, I felt a lack of a main character. Parts of the movie seemed to be the story of Fassbender's character, while others seemed to be the story of Rapace's character. Anyway, the supporting characters, to me, weren't developed enough. There seemed to be too many people onboard the ship to actually care about. Some characters seemed to be there just to be killed; two of them, especially come to mind as seeming hollow and just being there for the sake of showcasing danger. To sum up, I didn't really feel emotionally-connected with most of them. A smaller cast, like in Alien, might have been stronger.
The lack of strong supporting characters may have been fine, if the movie didn't suffer from it's biggest problem: an awful and muddled story structure. In the latter part of the movie, it seemed to lack focus, yet it tried to move at a break-neck speed. There were many tangents, which were made, only to be resolved quickly; to be frank, parts of it felt like a bad fan edit. Nothing seemed fleshed out. The story didn't have a linear progression.
Frankly, I'd be very curious to see if the deleted scenes; judging by how awfully this thing moves and the lack of development of some characters, I would think there are many. Hopefully, an extended edition may be made that would improve the film tenfold (like Scott's "Kingdom of Heaven"). I think this film would have been better with a longer running time and a slower pace. At roughly 2 hours, it was much too fast.
One final part which really irked me for some reason was the "Aliens" reference. I won't spoil what it was exactly, but I found it really forced. It just took me out of the movie. I didn't think Scott needed to refer to "Aliens" anyway, seeing how it was just a sequel to "Alien" and not really his movie.
Even with all it's drawbacks, I'd still recommend you watch it once, preferably in theaters so you can experience the full visuals. Hope I didn't spoil anything in this review.
5 out of 10.