Considered by Roger Ebert to be like being “trapped in a haunted house,” this film established a standard for summer horror releases. The design of the "Nostromo," similar to the spacecraft in "Star Wars," appears used and realistic, unlike the pristine appearance of vessels from "Star Trek." I enjoy the "Star Trek" universe, but the cramped feeling of the "Nostromo" is remarkable—a technique first seen again in “Das Boot.” A group of "space truckers" are roused from sleep to learn they’re only halfway back to Earth. The Company instructs them to examine an alien signal, which initiates a terrifying experience as the crew finds itself hunted by a predatory "Exomorph." As members of the team are eliminated, the creature's nature and the strange behavior of Science officer Ash significantly increase tension. This story distinguishes itself from other “space monster” movies through the character of Third Officer Ripley, who brings up unsettling issues regarding company practices—specifically concerning Science officer Ash—with Captain Dallas. Following Captain Dallas’ disappearance, Ripley takes command and uncovers Ash's real purpose, then leads her remaining crew into action. The film’s violence has been called "near pornographic," amplified by H.R. Giger’s disturbing Alien design. This is the initial installment of a noteworthy series of films, introducing a powerful female protagonist who appears again in the “Prometheus” prequel.

Source on TMDB