Nicely done
Incredible job for your first game. Addicting gameplay, but there were a few bugs:
1) Yeah, the men tend to automatically retreat, sometimes for no reason and when they have the upper hand at the beginning of the battle. It gets annoying.
2) When my units were clustered and I selected a group with a tank and attacked, 9 times out of 10 I ended up attacking with a regular infantry group. I don't know why.
Also, it would be a good idea to make more than one zombie model, rather than just color one model differently for multiple zombies. Visual stimulation, right? Other than that, great job.