This movie is actual peak in monster horror. What I love the most is how tension is built up through the slow pace of the movie. So when you DO see the Alien (not very often) it really freaks you out.
I especially love how little you see the alien, which sounds odd but the less you see a monster the scarier it is because you are now a perticipate in creating the fear! this movie may feel slow and boring for some but Ripley being a badass woman in the late 70s is a real treat you don't see often from these older films :)