Saw it and have to say that I liked it quite a bit more than I expected to. Yes, it's flawed and the pacing is a bit too brisk for a 2-hour film (it at least seems like there was some pretty judicious editing), but it's nowhere near as bad as it's been made out to be. To me, it makes for a good first installment and is begging for a better sequel. I think that Lindelof has been given far too much blame for the script when everything I've read seems to indicate that the ideas he infused into his re-write were mostly Scott's and that the script supposedly didn't undergo an enormous transformation from Spaihts's original. If I had to rate it, I'd give it a solid 3/4. It's definitely overstuffed and the "suprise" subplot and frankly the ending could have both easily been excised to make room for better development of the other ideas. Flaws and all, Scott's ambition is admirable and it's a damned sight better than nearly any big-budget science fiction film I've seen in years, including the "Star Trek" reboot, which I enjoyed but thought was flawed for many of the same reasons as "Prometheus".
I absolutely LOVED the design of the Engineers and the visuals were, in a word, stunning. One of my biggest gripes was the lack of development on the crew mutations and quite a few of the suppositions on what the planet was, what the Engineers' mission was, etc. were arrived at a bit too quickly and pat for my taste, but again, they didn't sink the film overall, and I'm super super picky 'bout my sci-fi. "Blade Runner" and "Alien" are still the gold standard for me, but Ridley has made a worthy entry into the cannon and probably his best film in many many years. And hey, it's gotta be better than "Alien Resurrection"....
Bottom line is, DON'T go in expecting it to be "Alien". It really is a different beast entirely and while flawed is damned good.