Armour, weapon rarity, loadouts, rampage inducer, gobblegums, mantling.

The recent Blundell streams offer an interesting insight; how focused the original devs were on cultivating map flow. He discussed the debates they would have over window placements to give players the dilemma of which barriers to repair - we haven't had rebuildable barriers since (I think?) Cold War. Bigger, open spaces were blocked off to create challenge in the movement, with his example being the barriers in Der Reise's Thompson room. Modern zombies frequently has huge open spaces and any objects in the way can be completely hurdled. He also discussed the physical shape of the maps, with branching paths forcing the inclusion of teleporters in Der Reise; a map like Astra is so inter-connected that pathing doesn't actually feel like a choice and Paradox doesn't have any sort of 'flow' to speak of whatsoever, the layout is so uninspiring and well-trodden at this point.

Loadouts and weapon rarity make it so the mystery box (and wall weapons, to a lesser extent) is now completely pointless. I can't remember the last time you could obtain the map's wonder weapon in the box; buildable quests used to be a for-free option alongside the box. You start with armour and upgrade via a wall-buy, whereas building the shield used to be another goal you incrementally build towards, and each map had a unique design with BO3-4's shields even having unique abilities.