Have a somewhat sort of "cache" Of ammo. If it's going to be a -shooter with limited ammo and needs to be wise- kind of game.
If not, then have so you have good fall-back defenses, or just defenses that prevent them from hitting you first and them hitting like a box or something blocking their path but you can still shoot them. have them all rangers or whatever unit is the human shooter, and have it a hero class. Obviously, you'll be somewhat better at shooting if you shot 100 zombies! Surly you can't get Worse at shooting
. Heck, this'll add some very useful abilities, such as an ability to have everyone in a radius shoot faster, run faster, construck obstructions faster,
A self defense melee thingy would be very helpful, such as for saving your sorry-self.
Have it so it's easier with teammates helping you, not nessicarly focus fire though, but like easier to take down zombies; And have it noticiably harder with the lack of a minimum of players ( like 3-4 ), just don't go extream hard.
Capn_danger has nice ideas, and I read, not everyones accurate hitting with a pistol, but since its WC3, Make an increase chance to dodge or miss an attack?
Traps is a very good idea, such as a certain character should be able to lay specific traps, such as slowing an area or someone multi-shooting a volley of like 2, or have an extreamly strong 1 shot kill every 3 minutes. Abilties to make the game more fun and possible. ( since the game of zombies should be realisiticly impossible )