This is not an Alien movie. That needs to be made very, very clear. If you go into this expecting Alien (or Aliens, for that matter), you will not be pleased. This is a different machine. However, the pacing is similar to the first Alien, so there's that. This is a movie intended mainly to ask philosophical questions that you don't fully realize were being asked until after you leave the theater. It does this very well while still holding your attention throughout the film itself. I'm still thinking about the movie now, after more than 7 hours after seeing it. The acting is effective (especially, of course, from Michael Fassbender as David the android), the script is overall good (although it does have one problem that I will address shortly), and there are many very good and interesting shots that stuck out to me.
The largest flaw that this movie has is a lack of characters that you can strongly relate to. Normally, this problem would be enough to kill any movie completely, but Prometheus only possesses it as a minor flaw because of the nature itself of the film and how it still works very well without it (which is pretty unique, actually). You don't care enough about the characters (there are some that you do care about, but just a select few), and that makes many scenes in this movie less shocking/impacting than they should be. If the movie allowed room for more character development and the like, then this would be an easy 10/10.
In conclusion: a great movie that just needs room for the characters to breathe. Bring on the director's cut, Mr. Scott.
Now, as I was saying, and Zac implies, from what I gather, this is supposedly set in, at the very least, an alt-verse in the Aliens/Predator canon timeline.
Since this was in the trailers, I don't view it as so much a spoiler, but look at the alien as it gets into that pod thing....look familiar? Looks like the dead alien they find in the crashed ship in the first Alien movie.
Also in the trailers, the design of the alien ship. Also looking familiar? Compare it to a certain crashed ship in the Alien movies.
Now, truthfully, I would be remiss if I also didn't state I haven't seen the film myself yet and probably won't until after it leaves theatres. Just not my thing, even with my interest in the various Alien and Predator films (to the point of owning them all, AVP films included)....just not the kind of thing I would spend $ to see in theater. Just so that is on the record.