alright thanks, here some suggestions
-more weapons and having the ability to put the unlocked weapons as secondary weapons and why not more secondary weapons.
-more enemies types, maybe a fast enemy that chase the player around, an enemy that can deflate if not pop, and an enemy pulling you closer to it to attack you, there's more but i cant say all of them
-more clothing and accessories for the enemies and players, like more details maybe like uniforms, armor, and hats, like example a police uniform for the enemies and players, so it will be not just normal clothing and even maybe some of them give defense from enemy damages maybe like the hazmat suit not getting effected by the green gas or liquid
-maybe give the players the ability to jump and sprint, is quite a bit boring and annoying to walk around if the map is super large
-a melee weapons
-a singleplayer story mode would be great, like explaining why the virus appeared and how the city going, like giving your game seems more alive
-friendly npcs maybe we can either recruit or summon allies to help us held off the enemies
-multiplayer, would be a great like to play with friends and can revive each others to make the wave to go even longer
-maybe a store in the maps so like players can buy like grenades, ammo, and health