I think Ridley Scott was very honest in his interviews that it isn't meant to be a "prequel" to Alien. It is, in its own way, but there's space/time between the two (ideally for more movies and exploration to be made). I enjoyed it because I didn't go into it expecting the ending scene of this movie to link up with the opening scene of Alien, I figured there would be differences b/c if this one does well, then it gives Hollywood an opportunity to cash in more on the franchise. My satisfaction bar was set pretty low, it just needed to be better than the last two Alien movies, and it was imho.
There were some areas that required suspension of disbelief, but all sci-fi movies are like that, so it didn't bother me. The only part I really took issue with, was when Noomi Rapace and Charlize Theron were running there at the end. Common sense would have said run perpendicular to the stupid thing, but again, it was done to reach a desired outcome so while it was irritating to sit thru, afterwards I was like "oh, I get it, ok" and it didn't bother me as much (altho Noomi still could have run perpendicular, but I digress LOL).
Michael Fassbender was absolutely amazing though! Loved him from the first second! Also interesting that he's the first of his kind, and already setting the "standard" for behavior for the franchise, which is perfect. Plus, with the way the movie ends, no one back home is going to know how that panned out (that it/they are a bad idea) and continue to use them, setting that up for Alien.
Overall, I say good, but definitely more theoretical/philosophical than Alien. A good set up as long as you view it in terms like Star Wars, that there are probably 2-3 more prequel movies before we get to Alien.