Pros:

Gandalf
LOTR Music
Horses!!
Requires teamwork to survive, and fun with friends.

Cons:

Perhaps add another heavy machine gun in the keep(my opinion)
Another suggestion: one of the npcs could ride one of the horses and charge into the horde of infected(again, just my opinion)

Conclusion:

Best map ever played!  This is just... EPIC!  The cons aren't really big, just some suggestions.