Sigourney Weaver battles a nasty alien that is killing off the crew of a spaceship. This is a good Ridley Scott film that is notable for the scene where the alien comes out of the stomach of one of the crew. This was the first of the series and the best. This changed many aspects of how sci-fi films are made. Ridley Scott said it was a monster movie but it had down to earth type characters rather than the super hero's of films like Star Wars which made it different. The film does benefit from some excellent effects for the monster and some good tension and shocks. This was billed as a monster movie in space, but it really more about the Signourney Weaver's charcter Ripley than the monster.
Sigourney Weaver
John Hurt
Veronica Cartwright 
Tom Skerritt
Harry Dean Staunton 
Ian Holm
4/5