L4D added a special twist to FPS (First Person Shooter) zombie games. They added 5 special zombies:
-Hunters
-Smockers
-Boomer
-Tanks
-Witchs
These 5 special zombies all added there own twist to the game. These zombies, are spawned in random places each time you play, they are spawned by the ingame director. Basicly meaning, the better you do, the more chance of finding a witch or a tank, and if you doing bad, there might be a witch, just out of the way.
In L4D2, there are a few new special zombies:
-Jockies
-Chargers
-Spiters
-Roaming Witchs (same a witch, just is startled a lot easier)
As a new twist to the in game director, L4D2, it can change your intire path by how well your playing; good, longer path, bad, shorter straight paths. This is to make the game harder or easier so that there is an endless ammount of difficulties; this is set by how good you are!
The demo was released last week for those who preorder it, and today for those who don't.