I've been enjoying L4D2; I still maintain that we were deceived and betrayed, but that doesn't make it a bad game.
Apparently there's an system of selection for the production of zombies:
"Regular folk" -the average humans of normal weight and height in boring clothing- become regular zombies.
Fat people that wear sweatpants become Boomers.
Skanky ladies become Spitters; I don't know what their skankiness has to do with having Acid Reflux, though. (Insert joke here)
Douchebags that wear hoodies become Hunters. (It seems like Hunters do more damage once they have you pinned. I think it's probably a buff to keep up with the other zombie classes.)
Really tiny people become jockeys (It doesn't seem possible that they're children, there aren't nearly enough. Presumably, Valve decided to remove children from the games to avoid frightening/concerning people with having to mow down waves of toddlers. This results in even worse thoughts afterward: if they're not around now, they must have been eaten. There's no way they could have escorted every single human child out of the infected area.)
Smokers become Smokers. (It's a good thing I'm here to explain these things to you people)
El_Dawg, from the El_Blawg, proposed the idea that people who abuse steroids/Human Growth Hormone become Tanks. Stay away from Baseball stadiums when the zombie apocalypse comes.
Emo girls become Witches. I wonder why so many emo people were hanging around a sugar mill for the Hard Rain campaign of L4D2? (By the way, Hard Rain is the best level Valve has ever produced, in any game. Some of the best atmosphere I've seen in any media.)
Tom Robinson becomes the Charger. I'm not sure where the rest of them come from.