Pros:

+ Great atmosphere
+ Great zombie spawn locations
+ Balanced even for scavange
+ Big and detailed, including even voice actors
+ Feels authentic

Cons:

- Autostart doesn't let you get to know the map before the match.
- You can easily get lost from your teamates when panic hits.

Conclusion:

Very nice map. Wish you did something like that with co-op

Pros:

Suprisingly fun
Makes me wonder if payload could work in L4D2
Awesome new concept
Creative

Cons:

Lack "get to da choppa" messages in the end led to half my team jumping down the hole leading to instant death.

Conclusion:

Cool map, cool concept. Worth playing, specially if you play TF2. If you dont, still worth giving it a try.

Pros:

Cool map
Creative
Fun
All kinds of zombies
Huge*ss hordes

Cons:

Much larger hordes can lead to massive lag
Sometimes it will lead you the wrong way into rooms with endless waves of zombies
No checkpoints - if you die, you are back all the way
You can see zombies spawning in a few areas. And since its right next to you it starts to get absurd.
Players get lost the first time they play.

Conclusion:

It's a cool map, and worth playing. Just had some trouble knowing where to go on the first time. This map lacks checkpoints - so if its getting hard for you, tune the difficulty down. Dying in the end and coming back all the way can be very frustrating.