In my opinion, a coop server/gamemode would be far more interesting than a CityRP(Deathmatch simulator), Super Murder Mystery(deathmatch simulator with a revival system, because some people don't know how to play at all), or a deathmatch(Sure, theres the occasional one with a unique build/weapons.....). Anyone remember Cucumberdude(I think thats who it was)'s Coop challenge server or Endless Zombies? I've seen only a few servers where you fight human-ish AI enemies(bots).
Side note
I've been thinking of doing a coop build for a while where you and 9 other friends go down a mountainside and fight AI bots that do NOT respawn when killed. Its finished, but Minigame events love to screw up when I reload a save. Instead of Onminigamereset-->self-->setbottype-->blockhead, its something random when I reload. Instead of Blockhead for set bot type, its usually a horse. Onbotkilled>Setbottype>None works fine, though.