Try and kill the alien by commanding the crew to move around the ship and carry out various instructions. The alien can be killed either by shoving it out of an airlock or by self destructing the ship and evacuating (only if there is nobody left alive). You have to take Jones, the ship's cat, with you. Mother, the ship's computer, won't launch the lifeboat if you've left anyone behind.
Three types of information are displayed on the screen for three decks on the Nostromo and you can obtain a map of any one of them. Each map gives details of room locations, stairs to other levels, and positions of grills.
Instructions are given to the crew using the Command Monitor. This enables you to select individual crew members and instruct them using a menu system, though the crew may not always obey you. Each of them has their own personality and if you instruct a queasy crewmember to attack the alien they may think twice. Another complication is that one of the crew is an android and you don't know which one it is.
If a crewmember is attacked by the alien, the map area fills with a large area fills with a large image of the writhing monster. This can be quite unnerving. There are a number of possible conclusions to the game. If you are ultra successful the alien can be killed with no crew losses. Alternatively, you can bungle the whole thing by running out of oxygen or setting the self destruct and not giving yourself time to launch the shuttle.
However well you do, the game remains exciting, nail-biting stuff. "In space no-one can hear you scream," the blurb says. My neighbours aren't so fortunate - I've been giving them a hard time. But who needs neighbours with entertainment like this.