I apologize but... Alien is not so much scifi as a horror flick set in space. I mean these guys were just intergalactic truckers on a lonely stretch of road. I liked Alien, it gave me the heebeejeebees and Ripley is to die for, but scifi? Not so much. For scifi watch Dark Star, Dan O'Bannon's early comedy complete with space surfing and supercilious intelligent bombs.
I've always thought of it as a sci-fi/horror mix, kind of lick Pitch Black, when it's taken in the larger context of the Alien franchise er... I mean Alien universe.
4+7, it goes up to 11
Or down to 3 depending on how you read numbers