Pros:

Cool maps and forces new strategies to survive.
Awesome upgrades, love the Anti-Tank gun :D
Gunships makes the world go round.
Support players are quite useful.

Cons:

Sandbox:
If I'm facing downwards when placing items, it falls through the map.
Base:
The cannon above the entrance should let me know where it is pointing to in some other way then pressing the fire button.
Mutagens have no way of being controlled and often go off at the worst time possible. 
Multiple items do not appear after being purchased, many times over and over.

Conclusion:

I love both maps, just love them. However several problems is annoying, the items going through the map if not deployed properly in Sandbox is a game-ender. In Base, All support upgrades worked well, however with the exception of Mutagens, very few of the weapons, health and bombs would show up after purchasing, and that's just depressing. I'll review again after any of these problems are fixed.

Pros:

A bloody good campaign, no less.
riot police amongst the panic attacks makes it harder :)
Easy to know where you're going
Awesome environment 

Cons:

none at all

Conclusion:

A great game overall, I rank this as one of my favorites that I'll keep playing again and again.
In fact......the only thing you could make it better is adding prisoner skins to the zombie horde (if possible)

Pros:

It offers all mutations plus some customs.
Organizes the menu so each mode mutation goes along the original.

Cons:

Nothing big, just a lack of description of each mutation.

Conclusion:

Beside from no descriptions, this mod is a must download.