Saw it yesterday. I loved it, yet was disappointed by it. My main gripe was the characters and their inconsistencies (Bill mentioned this).
Despite being just over two hours, the pacing of the film felt like an hour had been cut out. Aside from a few roles, character development was shallow at best. There were the "good" guys and "bad" guys, but their alliances weren't completely explained. I have no problem if they didn't explain it to keep you guessing, but the way it was portrayed felt like bad writing.
In spite of all this, if you have any interest in the film, definitely go see it. While it does leave many questions unanswered, it DOES answer the question I had ever since I watched the original Alien film so many years ago. That alone was worth the price of admission.********** WARNING: HERE BE SPOILERS **********
An example of inconsistent characters:
Take the two who were left in the pyramid (what they called it) when the storm arrived. At first, they reacted in a realistic manner when they found the bodies stacked in the hallway. Then they entered the storage room containing the oozing vases, and the mutated worms came. Now one of the characters is completely fearless, practically begging to be killed like an idiot in a horror movie.
Another example is when David has Shaw on the table, telling her she's pregnant, and then sedates her. She wakes to find two people prepping her for hypersleep. She fights them off (why didn't they give chase?) and uses the auto-surgery machine to remove the alien.
Then she returns to find David and some others, who seem completely okay that she escaped. In my opinion, this is a clear example of something that was left on the cutting room floor.
Another comment: While I love Guy Pearce in pretty much any other film, he can't play an old man to save his life...