-Helms Deep-

Pros:

-Amazing re-design of Helms Deep from the movie.
-Having Legalos leading the way is a great addition.
-Gives a true feeling of Lord of the Rings.
-Isn't to hard but isn't to easy which is great. Always a challenge no matter what stage your at.
-Custom made sword/shield and melee weapons.
-All-in-all definitely worth your time. It's something that you can continually play and not get bored of, no matter how bad you do.

Cons:

-Music removed, although there is a copyright issue I know.
-WAY to many tanks. The massive amount of tanks honestly ruins the gameplay for me sometimes, there's just too many of them. (the addon's biggest flaw in my opinion).
-Lag issues in the first 4 minutes is very common (even for my friends, not just me). Zombies will kind of instantaneously teleport to various directions etc. 

Conclusion:

This map is by far the best add-on to Left 4 Dead. It not only supplies you with amazing gameplay but unending fun. You can play it by yourself or with 3 teammates and all are equally just as great. It's not buggy (like some addons I've seen) and I have no trouble downloading it and getting on immediately. If your a Lord of the Rings fan and want to become apart of the real Battle of the Hornburg (Helm's Deep), this is the map for you.