Pros:

-Original and previously unseen mechanics new to the L4D universe, enemy survivors, lootable corpses etc. 
-Incredible detail in the maps
-Cut-scenes that give me goosebumps
-Custom models
-100% custom finale, a work of beauty might I add
-Witch skin doesn't override default
-Swimming pool! I love pools!

Cons:

-Several un-noteworthy visual hiccups
-Mildly confusing map layout 
-Item spawns the same each playthrough
-APC event didn't spawn horde, anti-climactic
-Areas where player could get stuck  
-Magical sewer lid in map 3?
-Still some low-res cars in traffic jam running event in map 2

Conclusion:

Finally managed to rummage up the time to play through 3.0, and I did see some improvements, namely tuning the nav meshes to cover elevated surfaces which did contribute a fair bit to my review score. And the elevator portion has also been tweaked I see, now survivor bots no longer slip and fall repeatedly. 
The item spawning still didn't exactly do it for me, too many health kits in map 2 and all throughout map 1 the item spawns were exactly the same each time, thus negatively affecting it's replayability. As well, maybe you should remove the hunting rifle in the spawn, because AI survivors will select any tier 2 weapon, throughout map 1 the bots we're entirely useless when dealing with hordes. 
Now, to expand on the map layout con, this is mostly geared towards the opening office in map 1, it's a rather large area and the only way down is by the wreckage, players instinctively avoid the burning ruins and instead wander the large office area in search of stairs, something to consider? 
During this playthrough I was pulled by a smoker into the box pile by the monument in map 3, once the smoker was killed I found myself stuck, this also happened in a playthrough of an earlier version, except in map 2, in the first military truck by the soldier. Not sure if the latter was fixed in this version but the former is still present. 
So besides these rather trivial bugs, I found that 3.0 is a significant improvement, you addressed many issues accordingly and I can see significant improvements, keep it at!

Pros:

-Brilliant scenery
-Custom skins and other content, shows how much effort you put into it
-Easy to understand and follow map layout
-Easter eggs 
-Expertly thought-out finale cutscenes

Cons:

-If I absolutely must select a con: I'd have to say that it didn't last forever

Conclusion:

To expand on my listed pros: The scenery of this campaign appeared to have a single theme, showing how the military and CEDA both reacted differently to the outbreak, and the opening in the church also giving the player a sense to the story with several other survivors holding out, but the four main survivors being the only ones who dared to leave what shelter they had. The skins and other custom content are mostly used in other campaigns as a sort of "lure" for players, but you implemented them without having them steal the show. The layout and pacing is just about Valve quality, never once during the finale did I stop and ask myself "where do I go now?", to me, that's a sign of a good map. Easter eggs are always a welcome addition, as long as they don't become redundant and over-used, I couldn't help but chuckle warmly when I saw that NPC reading "The Walking Dead" issue 39. Bravo on that. And finally, the cutscenes speak for themselves. I saw nothing notably wrong with "Warcelona" and I'd happily recommend it any day. 
Cheers!