Pros:

Challenging
Clear directions
Original Tron/Portal/Serious Sam test chambers
Fun traps
Waste space

Cons:

Bug in the finale elevator
Too hard in some places
Finale is not playable - at least for me - in single player. Anyway, I finished it with Gib Fest
All walls are black

Conclusion:

This campaign is for people who want to play L4D2 out from the urban or rural apocalyptic word full with piles of dead bodies.

Pros:

Side story panic events
Well done custom finale
The text and marks on the walls

Cons:

Hardly playable with the Gib Fest mutation
I saw no tanks in the middle campaigns

Conclusion:

A very good campaign with surprise events.

Pros:

The last duo on Earth mutations
A lot of L4D2 achievements can be unlocked using the training mutations and/or the realism ones
Jimmy Gibbs!
It is a guideline for new coming L4D2 add-on creators
Tons of other pros

Cons:

Few mutations are so hard that I could not advance more than few meters from the starting safe area.

Conclusion:

Keep your installation up to date, because - I am sure - you have this mutations mega-pack installed.

Pros:

Challenging onslaught events
Innovative (like the phone call)
Custom infected
Fidelity of the rural world

Cons:

Hm. I get lost many times, but that is my fault, I think.

Conclusion:

Play it and be prepared to die few times. This campaign is not about a refreshing rural tourism.

Pros:

Challenging
Multiple paths to choose from
Fine-tuned details
The bridge is simply awesome

Cons:

It crashed once, but who cares?

Conclusion:

This is a must to play campaign.