Ummm, I think you mean Call of Duty: WAW, not 4. Anyways yeah I love playing zombies. I've made it to level 26 with a group of 4 and I've made it to 13 or 14 by myself. Of course thats without any cheating.
Good news though for WAW, there are 3 new multiplayer maps and a new zombie map coming out next month. I think the new zombie map will have some new features as well. I think there will be some interactive things like being able to shock the zombies and there will be some kind of soda machine that is like the random weapon box that will give you different perks