Pros:

the soundtrack
custom weapons that aren't just reskins
cool ending scene (them on the train)
great finale
great maps

Cons:

no icons for sledgehammer or nail board

Conclusion:

amazing campaign but the weapons need icons

Pros:

mmmmmmmmmmmmmmmmmmmmmm nuttela

Cons:

i think i might throw all the zombie aside and eat it my self

Conclusion:

you're messing with dangerous stuff man

Pros:

challenging
interesting
l4d1 characters
custom voice acting
some German here and there 
YOU GET TO RIDE A TRAIN!!!!!!

Cons:

none its awesome

Conclusion:

it is by far one of the most well thought out custom campaigns i've ever played