Finally saw this last night. Alien is the franchise that got me interested in film making, so obviously I was hyped about this one.
My overall thoughts is that is was definetely good, but not as good as it could have been. It has some issues, most of which have been posted here already.
I agree that the final showdown with the Alien was too quick. Which also made it so that there wasn't really a sense of desperation. They found out there was a xenomorph on board, made a plan immediately, and it pretty much worked exactly like they planned on the first try. The sense of desperation in the original is incredible because they have all these ideas about how to deal with the Alien and none of it works. I understand that the movie was wrapping up and there wasn't more time for a lengthy showdown, but the xenomorph, the "perfect organism" being dispatched to quickly lessens the threat and impact of its presence a bit.
Speaking of the xenomorph, it was too fast, as in how it moved. This is more of a nitpick, but it's a detail that's important to me given my long love for the creature. Part of what makes it so scary in the original is that you can't really find it, it sneaks up on you. It's dead quiet until it's suddenly right behind you. Having it scream constantly and showing it run around with that speed makes it not as scary. I thought the shower scene was a perfect example of how they should have done it. It doesn't charge screaming into the shower and slaughter them. It sneaks up in the dark, does some really creepy shit, and then kills them.
I loved the opening scene with David and Wayland. And I thought everything up until landing on the planet had excellent pacing. It really took it's time with setting up the story, and it was great. But then the second half of the movie, while certainly entertaining, started to rush things, which is a shame because there's some really cool stuff going on. Like the time period from the captain getting the facehugger treatment to the first chestburster scene felt like it might have been 10-30 minutes, whereas in the original that thing felt like it took days to grow enough to burst out.
Pretty much everything having to do with David was great, easily the most interesting character and also the scariest of all the antagonists. Not monster-scary, but scary as in a much more sophisticated and calculating threat. Don't think there was anything wrong with the flute scene, I found it really interesting. Realizing David made the xenomorphs was a really cool moment.
And for all those saying that they "saw the twist coming", I honestly didn't even consider it a twist. Of course it was going to be David. Everything about how they filmed those scenes screamed it, so I don't really think it was supposed to be a secret, other than for the characters in the movie.
I'm sure I have more to say, but this is what I got right now.
At the end of Prometheus, she is bent on wiping the Engineers out so they cannot attack earth. I think she was definitely all in on the xenocide.
Shaw went on to continue searching for the answers they came for in the first place, not to wipe them out.