I bet some of you are thinking "Alien isn't even a horror movie. It's science fiction.". Yes, it is a science fiction movie but it has strong horror elements. I have always considered Alien a sci-fi horror film. The film has the characters facing the unknown, moments of isolation from the group, jump scares, darkness, body invasion, etc. It feels like a horror movie set in space to me.
I think ALIEN and ALIENS are great films. I have watched them both numerous times. ALIEN³ is flawed but I still do watch it occasionally; I have heard the original concept for the third film was to have an all out battle on Earth with the xenomorphs. That could have been great! ALIEN: Resurrection has some decent ideas but I enjoy that film the least out of the four. PROMETHEUS did a lot of things right but I can not help but feel it is also flawed. Finally, ALIEN: Covenant just felt like a wasted opportunity to me. For my ALIEN fix I turn to the numerous novels, video games, and the ALIEN Role-Playing Game.