The World War Z Update, obviously, is so named because it should be heavily focused on zombies, and turning them into the unliving death machines we all need in our lives. First, zombies can spawn a million others, like in the snapshot in which it came out. Second, the zombie's spawn rate should be raised, making zombies a much more common site than creepers and whatnot. Third, if enough zombies are near eatch other, they can make a "zombie tower", and bypass an obstacle. Although this may be true, a certain number of zombies are needed to do so. For example, a zombie tower capable of climbing over a 10 block high structure can also climb over a 5 block high obstacle but not a 11 or more structure. Fourth, if a zombie attacks a villager and DOES NOT kill it, the villager WILL become a zombie within a day. Last but not least, zombies are almost completely immune to explosive damage. Just some suggestions.
Minecraft is not a zombie game. It is a sandbox/survival game. Also, Mojang would get sued by the people who made the World War Z movie because of the title. Regardless, this would make zombies waaaay OP.
Or just haven't played 1.6.1.
"On a scale of one mile to Lord of the Rings, how far did you walk today?"
Zombies are good as they are, no support.