Pros:

Greatest L4d map EVER!
...
Scratch that, greatest Video game add-on ever created!
Amazing.
I just cannot express how awesome it is.

Cons:

The only Con I can think of is that the NPC's (i.e. Gandalf, Legolas don't move)  Even better is you could reskin the players to be the characters from the movie.  That would would make this the highlight of my life.

Conclusion:

Sick map bro!
I'd like to see it made into a campaign mode.  You could find out how many zombies you killed!