Even when you leave the infested portion for good, you're still jumpy, waiting for the next alien to come out of the wall and have at you, and those orchestral stingers in their wake sounds don't help much. There's also some eggs, very creepy, and a surprise encounter with a facehugger (and an alien!) in the cramped and poorly-lit air duct system. Sure, you could kill them up close, but there's no telling what's going to shower you with acidic blood when it dies. The thing placement is wonderful here, creating obstacles that don't really impede your movement until you're trying to evade the dreaded aliens. More tension mounting until you reach the meat of the level, the infested base. The things that generate ambient noise and comm messages are genius and help set the mood as you explore. It will make the following maps much easier, though. I mean, you won't need it here – there's nary an enemy to be found, just tons of atmosphere as you explore the deserted exterior of the base. There's nothing to find here except some desperately needed ammo and armor.

Aliens the ultimate doom