Things I think that they should inclue:
-Forge gamemode. (Where you can edit and make your own maps)
-Bosses
-Zombies with guns
-More than 4 players
-Be able to play splitscreen online. Me+my friend with some other people online for example
-Safe areas, that cose points
-Be able to pause online (for points)
-Be able to be black on zombies
-Zombie animals diffrent to dogs
-Be able to buy backup
-Killstreak rewards (100killstreak = Assasination squad for 1 round)
-Have team mates in single player