if cod 7 is definatly getting zombies then i will be buying this game just for that since i love wave defence games main things i want are
1.as close to modern weapons as possible m16s,m4s, d eagle etc
2.ability to customise the weapons (maybe have a lucky dip machien that you pay for to get a random attachment or they could be drops from zombies)
3.rewards for maybe a head shot kill streak or knife kill streak e.g. ammo crate that everyone can share for a limited time
4.zombie counter so we know how long/how many got left
5.ability to set up a small defence position e.g. sandbags/tables or whatever fits with the setting of the map (obviously at a big cost so not to easy to get them) to help defend in later levels or even just so you have a place to allow players to setup support guns using bi pod or somthing (obviously make it a little time consuming to set up/exit so as to make it a bit risky when zombies get to close
6. a call for help button when down for people who dont own mics
7. someone already suggested the idea of being able to spend points to upgrade window defences to make them stronger and last longer
8. riot shield would be good could use that instead of the number 5 idea
i dont think the idea of makeing a map with the ability to go outside or all over the map is a good one as i think it would cause people to just end up spliting up and getting killed