The third Gearbox Software developer diary for Aliens: Colonial Marines goes into detail about how they plan to build tension, using original assets from the film to create a real sense of immersion. As an example, the motion tracker uses the classic "ping" sound effect, which should lead to some unbelievably tense moments as the Xenomorphs approach. Nine metres. Seven. Six. That can't be... that's inside the room.
In the previous dev diary, Gearbox revealed that aliens have "big, nasty mouths."