While technically not a prequel, Premetheus does take place quite a bit before the original Alien. Without divulging too much of the plot, suffice it to say that many questions will be answered by this movie. Some of those answers are pretty surprising. This movie is much more sci-fi than horror, although there are some gory bits. It is not as scary as Alien, but there are some "edge of your seat" moments. The special effects and cinematography were outstanding, but I expect that from modern sci-fi movies. The acting was superb, especially Noomi Rapace and Michael Fassbender. Both were extremely believable and the rest of the cast performed well also. What I wasn't expecting was just how philosophical and thought-provoking this movie would be, but that was a huge bonus in my opinion. While Prometheus didn't feel fast-paced, when it ended I didn't feel like over 2 hours had gone by. The only complaint I have is that I think the 3D could have been better utilized.
Pros well paced, great story, great actors, outstanding special effects