So, let's take Aliens as an example. What's cool about Aliens?
Well, it's scary. But why?
The Aliens typically attack people in situations where there's little or nowhere to run, and there's no way to get help quickly. Isolation to spur terror is a big part of the genre… no one is coming to save you.
The Aliens are a primal, predatory force. The more you know about them, the less scary they are (knowledge and details about your opponents makes them less threatening in general), so when introducing them, it's best to keep them as a nebulous, predatory force that serves as an adversary to the player.
Next, the threats in Aliens are actually two-fold. One is the aliens themselves, which are shadowy, nebulous threats lurking in the dark. The other threat is the human factor – routinely in the movies, it's the human psychological element that causes the secondary, and usually greater, threat. One could argue "the company" is basically another, equal shadowy nebulous predatory representation of the aliens. As an example, Burke's greed in Aliens is a huge threat. Hudson's panic is another. Gorman's arrogant by-the-book incompetence is another, his unwillingness to admit he's in over his head nor that he is unfit to command. Apone follows stupid orders. Vasquez is recklessly berserk, and her keeping her storm gun in Aliens and opening fire during the first encounter in the Hadley's Hope nest actually sets the timer limit on the detonation in the colony. Dallas in Alien is clearly apathetic about following the company's directives, and his apathy puts the crew in danger. Parker in Alien wants his share, etc, etc. All of these human elements serve to create equal, if not more, significant problems for the player. So having the human factor as a gameplay elements is equally important, and it should be tied into NPC and PC psychology.
Now, let's take Ripley. Ripley is the hero, and her strength is her perspective on the situation (usually the smartest perspective – "nuke them from orbit"), and her ability to take the psychological handicaps of her crew and immediate party members and either course-correct or overcome them (Hudson's fear, Newt's catatonia, Hick's unwillingness to step up and take command, Burke's sliminess, Ash's company loyalty, etc.). So this also seems to be an important part of the franchise.