The only reason that the zombies get anywhere in here is that the sim civilians are too retarded to run from a moaning zombie. Since they're happy to walk up to Zack and give him a big hug, that pretty much negates the classic zombie disadvantage of bad foot speed, neh? Not very 'simulation' ish.
Good first draft and a solid fun game. A lack of different maps and more 'stuff' (enemies, allies, turrets, gear) keeps it from being a real standout, but could easily get there.