Pros:

Minecraft-based campaign.
Had to do some crafting to progress through some areas.
Great design.
Some surprising easter eggs (at least I think they were).
Couple of surprise appearances of Minecraft mobs.
Fun finale.
No noticeable bugs or glitches.
Bots were actually useful.
Minecraft Music, and dark cave noises at certain parts.

Cons:

It's not on L4D2!  (Won't take points away, though, hehe)
Other than that, none I can think of at this moment.

Conclusion:

Fantastic Minecraft-based campaign for L4D1.  What can be said, besides this was one of the best custom campaigns I have played on L4D1, and would definitely play it a quite a bit more.  If you're a Minecraft fan (or maybe not), would recommend anyone that owns L4D1 to check it out at least once.

Again, fantastic job, and great campaign.

Pros:

Freakish, gross, scary.
Fits perfectly into the L4D universe.
No errors, no crashes, nada.

Cons:

None, really.

Conclusion:

Fantastic skin for the boomer.  It reminds me of something similar to the fat zombie out of Doom 3.  I love it.  First time I saw it on here I said something to myself along the lines "oh, that looks pretty cool."  Then when I installed the skin, and saw the boomer, it wasn't a pretty sight to look at (most zombies aren't, lol), and fits fantastic into the L4D2 universe.

Highly recommend it to any L4D2 player.

Pros:

Works good.
It's another shotgun!

Cons:

Have had problems using Explosive / Fire bullets.

Conclusion:

Seeing how I'm still using the version of this mod before it was changed to make it 'not so overpowered,' it's still pretty awesome.  Had some weird issue when using Fire/Explosive bullets - almost like it was shooting a single round off to the lower right of the crosshair.  Was strange, but aside from that - pretty good stuff.

Pros:

No crashes as far as I've noticed
No glitches as far as I've noticed
Good quality.
Total re-skin

Cons:

Most of the cons are pretty much listed in the description for this skin.

Conclusion:

Aside from there not being any facial animations, fps arms, custom animations, and other stuff that is listed in the description, it is one of my favorite skins for Zoey.  Not just a nude, or changing or jacket, hair, etc, but a total re-skin of her.  And I have to say, I love it.  (Also brings back some memories of playing WoW.)

Pros:

Freaky, creepy.
Awesome textures.
Fantastic Quality.

Cons:

None.

Conclusion:

If you're someone looking for new skins for the Special Infected, be sure to pick this one up.  Fantastic quality, and isn't just some half-assed re-color of the smoker.

Pros:

Works great.
Good Re-skin for the tank.
Um, did I mention it's great?

Cons:

None that I can think of at the moment.

Conclusion:

Pretty great re-skin for the tank, better than some of the few others that are on this site.

Pros:

It's the Duke!
Works great.
Has Coach's name changed to 'Duke.'

Cons:

No Duke sounds, makes me sad.

Conclusion:

Pretty awesome skin, haven't had a chance to play coach in first person, but everything seems to be working perfectly.  No crashes, glitches, nothing at all.

Awesome skin, use in conjunction with some others, almost makes L4D2 feel like a whole different game.
Also, if you're a duke fan, get to downloading this skin now!

Pros:

Awesome
It's Duke Nukem Music
And...well, awesome.

Cons:

None whatsoever.

Conclusion:

Surprising that more people haven't downloaded this tank music mod.  It's just plain awesome.  Oh hell, it fits the tank more than the default music.

Pros:

Works great.

Cons:

While looking at her from another character, it doesn't show the streams of vomit after being puked on by a Boomer.
No facial animations.

Conclusion:

It's a fantastic skin, especially for anyone that is a portal fan, or just looking to have a group of characters from other games group up to kill some zombies.

A shame the only two drawbacks (as I stated in 'cons') I noticed was that it didn't show the vomit on her after being vomitted on by a boomer, and facial animations.

Other than that, if you're one that can live with, or don't much care about those two drawbacks - it's a must download.

Pros:

It's Alyx!
Great detail, nice cleavage.

Cons:

Like the others, no facial animations.

Conclusion:

Fantastic skin, works almost perfectly - except for the facial animations.

Pros:

Fantastic Mod
Lots of replayability.
Tons of mutations.

Cons:

None That I can think of at this time.

Conclusion:

If you're going to download anything, make sure it is this mod.  It breathes even more life into L4D2.  Why play the old boring Campaigns, regular versus, realism, etc.  This mod brings some mutations to really mix up the game play.  I highly recommend it to anyone that is a casual player, hardcore player, any L4D2 fan out there.  This is a must have.

Pros:

Great campaign
Good versus play

Cons:

Seemed a bit short (maybe that's just me).

Conclusion:

Overall, I pretty much loved this campaign for versus play.  The ending finale reminded me of Cold Stream's, which was one finale I really don't like at all.  But, other than that, it's a very fun campaign, not all too long (compared to some other custom campaigns), it's definitely worth playing over and over again.

Pros:

It's Mario
Great campaign
Very well executed
Very fun.

Cons:

Bots are god awful at staying alive (especially true in the 3rd map)
Tank music not playing at the Finale when the tanks spawn / arrive / attack.  Whichever.

Conclusion:

One of my top favorite custom campaigns to play, especially online.  Seeing a human player fall to their death while trying to make a jump for the moving platform is just hilarious.  Really a great map, and I highly recommend downloading it to any Super Mario fan out there that plays Left 4 Dead 2.