Infection would work like this. Humans would have to survive from the zombies, and when they die they become a zombie as well, and the game would end when everyone becomes a zombie. Don't know why the zombie game mode isn't like this already.
Right now it isn't even zombies anymore. It's just a bunch of super jumping humans with shovels trying to steal the intel from the team that can use guns while that team steals the intel from them. Its basically ctf, but one team is can only use a shovel. Kind of ridiculous.