The game is already lots of fun and ou have something quite good in the making!
some points from my side:
+smith and w. weapon: longer reload should usualy mean higher impact. 6 bullets would work if they could kill instant.
+chainsaw: higher range and a "hold" mode (as long the button is pressed the chainsaw gets hold infront of you). i would also make it a "special weapon" (just one per game for all players and very powerful). run it on gas and let it disappear once the gas is gone.
+hp: i dont like the madipack idea. something where all players can leach hp out of an item after the round would be nice. so they have to "share" a limited amount of hp recovery...might lead to nice situations
+hitzones: a must have in such games. i aimed at the heads of the creatures quite some time, till i realized it doesnt have any effect (yet?)
+spell range: add some spell range to the fire effects. the game is hard enough.
+fighter classes: maybe worth a thought to add different player characters (medic, soldier aso) different stats and some unique skills. only the soldier can carry the rocket launcher but only the medic can heal aso.
+traps: some puddles filled with gas, some explosive charges or boxes that get lit by shoting it...
+goodies: shields, speed reloads, fire ammo....time framed upgrades
+not dead: when heelth reaches zero, add an option that some teammate can heal you during a short time period. it might lead to players risking their lives for others.
+different crates: add some variation to the crates for tactical reasons. iron crates last longer, trap crates kill the zombie when they collapse, gas crates slow down enemies in a range aso.
+crate on crate: minecraft anyone? piling crates right now doesnt help anything. why not "create" new crates by putting one on each other. wood crate + iron crate = spike crate. spike crate (hurts touching enemies) + fuel crate = buringn spikes crate (hurts enemies in range)....aso
+changing enemies: maybe the enemies could interact too. for example a ghoul kills and eats a zombie and becomes a zombie ghoul with new powers or a fire ghoul when kill on of the fire thingis.
+boss mobs: you know it and we all do: you need some boss mobs from time to time
just a few ideas
keep up the good work, this might turn into quite a good game!
cheers