Also: death sequences, where the alien doesn't kill you, but it corners you and the screen fades to black, followed by a series of horrible screams as something happens to Amanda.
Screams from people being killed in the distance. Random screams.
Random power failures and other disasters that you would have to contend with in different ways.
Teamwork -- Ripley, Parker and Brett-style.
A paper map that you would have to unravel and read on the table, just like in Alien, except try doing it in the dark with a flashlight.
Side-quest encounters with Ransome and other DLC-characters (optional, not mandatory).
The ability to commit suicide with explosives if the Alien grabs you, like in Aliens.
The ability to pick up and throw objects, like coffee cups and containers, to distract the Alien quickly.
Instead of powering up parts of the station, have instances where you'd have to power down the station and navigate through areas that are extremely dark. Or, explored internal parts of the ship with no oxygen, requiring you to suit up inside the station. You'd be unable to run away from the creature and it'd be tense as shit.
The ability to capture facehuggers and throw them at looters (lol).