Left 4 Dead 2 is exactly like the original Left 4 Dead and should have just been a patch! Oh wait, it's not. The five maps, four characters, new weapons, new director and new zombies look pretty substantial to me, and here's a few more extras, as found in GameSpy's Left 4 Dead 2 preview.
First up is a brand new special infected, known as The Spitter. As you might have guessed, The Spitter provides its infected brethren with a bit of firepower, able to spew up area-of-effect damage from its mouth. Speaking of infected, the hazmat suit guy we all saw at E3 was the first of what Valve are calling the "common uncommons." These are infected that have unique traits, but aren't special infected, and each chapter will have its own type.
The swamp level previewed had a brand new "uncommon," known as a "mud man." These are crawling zombies that skitter speedily along the swamp floor on all-fours. It is said that these uncommon infected really help to change the way each chapter is played, requiring extra vigilance from players. Mud men sound creepy, for sure.
Apparently, health packs and pills have been entirely replaced by adrenaline shots and ammo packs. The former provides a speed boost to players and allows them to indefinitely abuse melee attacks, at least until it wears off. If these items truly do replace health, this could be one difficult game. We'll have to see.
Destructoid itself shall be taking a closer look at Left 4 Dead 2 at the end of the month. Stay tuned for our own discoveries soon!