This game needs some work (balancing). First, the game was too easy. If you strictly buy German infantry, it wont take long until you wont take long before the bots will take care of the entire level by themselves. The units are very unbalanced. Why are the units separated by country with such huge differences in DPS? I'm not a history buff, but im pretty sure American troops werent a bunch of craptastic soldiers in comparison. Could have added grenadiers, and what not instead of just infantry and MGs. The personal guns were garbage too. The 2nd to last gun had a higher DPS than the thompson (for half the price, calculated by dmg/rate of fire). Anyway, the zombies and the game in general was just too repetitive. Only reason i finished it was out of pure boredom.
TL;DR: Game needs balancing: unit and difficulty balance. Decent game, needs polishing.