Got to see it last night.
Overall, I think it's a great sci-fi thriller. Visuals and music are gorgeous, the acting is solid, and the story and questions it raises are very interesting. I'm glad Scott didn't abandon the ideas he was exploring in Prometheus, although the movie feels a lot more like an "Alien" movie than Prometheus. The entire opening sequence is really cool in setting up the themes that will be explored throughout the movie.
It raises questions about love, duty, faith, the disappointment of children when they outgrow their parents, and, of course, the dangers of AI.
As an "Alien" movie, it's just not scary enough, IMHO. I think Scott just doesn't know how to make a truly scary movie anymore. For all its length, I felt it never took the time to really scare you, to just build up that dread of the first movie (and arguably the second and third).
That's not to say it doesn't have very tense moments and lots of excruciating gore, it has lots of that.
Fassbender is great, unfortunately Waterson doesn't have the charisma and presence of either Weaver or Rapace, which is a shame. The star here really is Fassbender as Walter/David, all others are just along for the ride. Nevertheless, I found this crew had more character that the Prometheus crew, and I felt more for them as each faced their inevitable demise.
The creatures were great, I especially loved the neo-alien. Truly scary beast.
Going back to the movie as a whole, it also seemed like a "hommage" of sorts to every single alien movie. I saw references and visual cues to Alien, Aliens, A3, Alien Ressurection and even AvP (no AvP-R, though, thankfully), which I thought was pretty cool.
So, again, it's a great sci-fi thriller, maybe a little lacking in scaryness in order to be a great "Alien" movie.