I've played this map a few times, mostly with friends, and I quite like it. Some suggestions, however:
-The zombie attacks, while initially quite hard to defend against, are eventually defeatable by one player. At the end of one game, I was holding the trenches all by myself. If they gradually increased in numbers, it would put a lot more pressure on the players to get ahead and win - and create a much greater atmosphere of a desperate band of survivors holding out against the zombie hordes, etc etc.
-The Soldier and Bowman both share the same icon, which can be confusing at a glance. The various builders also all share the same model, which can be even worse if you're trawling through a whole city to find one.
-Some upgrades for the human players would be good, particularly for whichever unfortunate soul has to hold the border.
-Finally, rat attacks in the cities can be... annoying. Why would a rat hit four times harder than a man with a sword, anyway? It would be better if you replaced them with some kind of weakened zombie (infected by the airborne strain of the virus, perhaps) and randomised where they spawned in the city.
Other zombie ideas - a support zombie (undead priest), a weak-but-fast one, and one that gradually corrupts the land behind it, causing damage to troops in the area if it is not purged.
All in all, though, I really liked the map. Keep up the good work!
