Pros:

Great textures.
Great model ( even has drum style clip ).
Authentic "Chicago Typewriter" firing sound.
Breath of fresh air for people like me that have been wanting this gun in L4D2 ( I mean come on its a tommy gun vs zombies how cool is that?! )

Cons:

This isnt really a con but worth mentioning. Some people ( such as myself ) have to manually install the vpk file in the l4d2 add ons folder, even though when you double click it, it says its installed. 

Go to Extras and check add ons to make sure the mod and sound are listed.

Conclusion:

With great modeling, skin / textures and an easy to install this gun gets a high rating!

Pros:

AS AMPLIDUDE SAID : 

======= In general =======
+ Great setting in level 1.
+ Great setting for the rest of the 3 maps.
+ Snow is freakin' awesome.
+ Nice surroundings.
+ Survivor dialogues.
+ Creative through and through.

Cons:

======= Map 2 =======
- Freezing point for AI on the great wall.
- Over exaggerated panic event in SP.
- Great Wall was quite small compared to other Great Walls in other campaigns.
===================

======= Map 3 =======
- Melting points for the ice can be hard to aim at.
- Charges just went straight into the water with mates of course.
- To heavy task for SP on advanced or even expert.
- Rescue music appeared although task wasn't fulfilled yet.
- Lack of all kinds of supplies in the finale made it too hard to survive.
===================

======= Miscellaneous =======
- AI mates loved to fall off the Great Wall.
- Short, but okay for 3 maps.
- Please more supplies.
- HARD TIME FINDING FIREWORK CRATES WHEN VISIBLE SUPPLY WAS USED UP.
=======================

Conclusion:

Sorry to be lazy but pretty much what AmpliDUDE said I experienced, except the crashing. I had to use sv_cheats JUST to try and survive on advanced mode. However the unique finale was VERY creative, yet VERY difficult and not in the "player is a noob" sense. 

Pros:

1.Brings a cultural favorite of the zombie genre to L4D series.

2.Looks just like the character from Dead Rising series.

3.As with all custom add ons / files , it brings more variety to the game.

Cons:

1.A minor con only, mouth doesnt move when speaking. Not really THAT big of a deal except for the most extreme of players.

Conclusion:

Overall I dont see any problems with it ,save for the very minor mouth detail not speaking with words which ALLOT of people will overlook especially while fighting in game. This is easy to let slide as , unless you are looking at the face up close you dont notice it, which is 85% of the time.

Having said that, the pros heavily outweigh the minor cons.Also I give big props to anyone that can model / skin / map as I value their contributions , highly.