A few thoughts: It feels like a cop-out, but I almost don't even want to write this review at all. Alien is one of the most well respected sci/fi and horror movies of all time, and my thoughts on it don't vary much from that label. The cast do a great job at feeling like actual people (unlike the over-simplified action sequel) trapped in a claustrophobic setting. Every character behaves as you might expect, which helps heighten the suspense. The setting and creature design is beyond terrific, with great special effects and a perfectly complementary musical score that adds to the tense atmosphere. I didn't initially enjoy this movie (don't ask me why, I was probably just being stupid), but every single rewatch since then has improved it in my eyes. This is a fantastic horror movie, an equally fantastic science fiction movie, and a total masterpiece of suspense. Easily one of the greatest monster movies ever made, and far superior to the sequel -- which I still enjoy, it's just much less interesting. Oh, and yes, this movie did inspire my website color design.
Who would I recommend it to? Fans of science fiction, monster movies, horror, and thrillers. It has a fairly general appeal that can't be missed by a majority of moviegoers.