Finished playing the Zombies mode with my brother, don't know stuff, but it seems like a combination of all the bo2 maps.
The harvesting pods was inspired by digging in origins. Shocking/beast mode inspired by Mob of the Dead Afterlife. Believe it or not, i didn't even know that Beast Mode until i watched a few videos after playing. They should have done something so when you spawn, you are in Beast mode which gives you a idea what it is. Especially for new players.