I'm pretty sure it said that the avogadro was one of maxis' experiments or something and you must harness his power on maxis' side.
Mob of the dead was made to be similar to call of the dead, obviously, but this time it doesn't connect to the main characters it just has its little side story, I hear it was to give the zombie team time to make the 3rd and 4th zombie map and finish the story line. It honestly is a great story and map but it is easy to play. They are not in hell, they are in purgatory meant to live out the rest of their existance in that moment of the attempt to break out of jail. The map doesn't really have a time, besides the time that the jail guard says they were executed. As I said before, they are in purgatory and for all we know this could be happening during the old characters, the new characters, and the next characters because it is a forever repeating cycle till the end of time.
Buried: who said it was in Africa? that is news to me, I'm pretty sure it is in the mid west but I haven't honestly paid attention to location
Nuketown: didn't they release it with the purchase of the 4 map pack deal? Not too far from tranzit release/game release
I personally think the story is amazing overall. It is continuing from BO after the earth is destroyed. what is the old crew going to do, run around with a little girl trapped in richtofen's body? nobody wants to play with that for 4 more maps. It moved from the fear in BO to major storyline and I like that. The suspense is crazy about who they are and we slowly learn about them through maps, what do you want to know more about them, their birthdays and hobbies? What matters is that they are the few survivors left and they have been chosen to do these quests for maxis/richtofen. The amazing thing is that, though there is speculation, NO ONE KNOWS EXACTLY WHAT IS GOING TO HAPPEN NEXT. What the heck can they do after End Game?? It is so exciting!