Alien is by far one of my all-time favorite movies, and it absolutely DEFINED the scifi/horror genre. None of the sequels (especially the James Cameron sequel, but I don't want to rant on why it's inferior) came close to the innovation and near flawlessness of the film itself, or give the sense of sheer dread that the first one did. Marines and Predators be damned, the original will ALWAYS be the best.