The Zombie's in H-L are Scientists with a Head Crab on it (In Opposing Force, there are also Barney and Human Grunt Zombies). They haven't changed much.

zombie.jpg (34134 bytes) The oldest form of the Zombies that I know of, the only real differences is that more detail was added

zombie0.jpg (25148 bytes) This is pretty close to the current version, but for some reason they are blue

zombie1.jpg (48121 bytes) From this pic you can tell much more detail was added

zombie2.jpg (6076 bytes) This pic shows some more details were being added before it was finished

zombie3.jpg (9430 bytes) Another pic of a low detail Zombie