Pros:

EPIC!!!
Extremely detailed.
Outstanding looks.

Great atmosphere with custom sounds
(don't forget to do the snd_rebuildaudiocache).

Multiple paths (which is in fact a pro for playing it more than once) and some of them are even blocked sometimes like in L4D2.

A new well done escape vehicle.

Cons:

Minor bugs that will be fixed anyway.

Conclusion:

Valve should reward this with an expert achievement!

100 just isn't enough compared to others. So I give it an unofficial 150 :-P

Pros:

nice detailing, nice locations, nice events, nice graphics and effects, use of random paths in sewers, good finale

Cons:

already played it too often :-D
(following the development closely since L4D1)

Conclusion:

one of the best campaigns with a great variety and a professional touch

(more infected on the way back to the helicopter and maybe a tank guarding it would be nice)