Alright, lets define original zombies.
There are about two types. Slow and Normal/Fast.
A Slow Zombie is one that has been rotting in the grave for quiet some time, but have risen from the dead. They are slowly decomposing and missing limbs so they can't run as fast as a "fresh" Zombie.
Normal/Fast Zombies are infected individuals. They have either been bitten and have turned into a Zombie, or they were recently killed and brought back to life by the undead plague.
Each Zombie has three to four times the amount of health of the average player, but can be put down by two headshots. (One is just too easy considering how large a Blockhead's head is.)
The only type of "special" zombie that is original - that Mr. Noßody mentioned - is a zombie missing it's lower half. The pants node and the feet nodes. They move with a slow crawl. But they have the advantage of not being detected among the waves of undead, since they are crawling.
This basically sums up my idea of what original zombies are.