It doesn't just count how many baddies you killed, it monitors your emotional state, taking into account what it feels like to be knocked to the floor, have blood splattered in your eyes from a point-blank headshot, lose a friend, get strangled, pinned down, vomited on, trapped, delirious with pain. Not to ensure these things don't happen too often, you understand. No, it just wants you to go through them all before it lets up.
Left 4 Dead is all about those classic moments, and it's uniquely suited to them. The traumatic misfortunes the Director tracks are mostly things your friends can save you from. You can cut a teammate down from the noose-like tongue of a rooftop boss Infected as he gasps and spasms, offer your hand to a friend who's blasting away at the hordes on his back because he's too injured to stand by himself, and even pull a buddy up from a precipice they've oh-so-nearly fallen off. If you don't reach them in time, they slip from their elbows to clinging on by their fingers, then dangling by just one hand, before finally dropping to their doom. It's brilliantly cinematic.
The Director is harsh, but it's rare to die from the bloodthirsty crowds. No, it's the bosses that kill you. Survival depends as much on keeping your head as your health, and it's the boss Infected that can blind, strangle and trap you. When one player's down, it's all too easy for your team to fall apart. The others can help him up, but stopping to do so usually means failing to notice the other boss lurking in the shadows. Soon you're down two men, and at that point you're in serious trouble.
The most terrifying of these bosses is the Hunter - not to be confused with Episode Two's robo-alien. He's just a guy in a black hoody, except that he can leap 60 feet in a second. If you turn your back on him for a moment - and it's hard not to given that he's invisible until you shine your flashlight directly at him - he can jump at you with a howl that makes your blood run cold, and you're utterly helpless as he scratches at your face. We physically flinched every time this happened to us.