More Zombie and enemy types. Not just human-zombies, but even more original AI like zombie dogs, vampires, archers, knights on horses, raptors, enemy soldiers that can pilot tanks, etc. The more variety and custom AI you have, the more likely people are to download your mod or make AI that relies on it.
Rot-mod like tank model (this is seriously the only reason I use his instead of yours, other than the fact that bug mods need it)
Tank Bot. I really want a challenging fight, 1 v 1 with a tank, on single player.