From the description it sounds like there are going to be different objectives that your group will have to complete on each map. I think the enemies keep spawning after you kill them so you will have opposition while you are trying to complete objectives.
Hopfuly thats true becacuse that would be alot funner.
From what I gather, it sounds somewhat like zombies, the enemies may spawn in waves, or just constantly, but whatever it is, it will be fun and i can't wait