A lot of things need to be done to make good apocaliptic feel main things:
-Scarce on weapons, not that you go trough and after 30 min you need to empty your back pack at shop because it's full.
- Ammo, god fukkin ammo you shoot by burst, you can ask what it's wrong with it, well if there is an apocalypse next door, between "The normal ending of world by nukes or other shit" and "The Apocalypse" is a big mess, people shooting each other at sight looters burning Weapon and ammo factories highly raped, also what force (raiders, army outcast, last remntats of army.) cannot haul, from the weapon factory, will be destroyed in time where is no moment to think about future, where the end is now. so the ammo in theese times would be very hard to get, so think about 20-30 years later, the apocalypse where last points of ammo (Gunstores, small factories, some ammo packs found in the rocks of destroyed factory...) don't exist anymore. To make it short, there should be 2 types of ammo, good old world ammo- very hard to find. and new handcrafted ammo, from weak smelts and shitty gunpowder. This is where player decide if he risk his life with weaker ammo, or give all of his money to shopkeeper for some bullets, some games tried do it like that, but they did not balanced it well, the weaker ammo should jam weapons, sometimes there should be misfires and other thing to show the weakness of new world stuff made of junk.
- Back to the roots - When technology is no more, we get other weapons!, bows and crossbows should be in here for sure, also full kevlar/metal armours. and when that tech comes back, the crazies shows their asses and welcome the King's Arhtur's Madmen!
About Gameplay...
Looting - This is the shit you should spend most time, not fighting stupid raiders.
loot places should be time based, like when you search it takes time, and areas of loot (Here comes hard thing to decide) should, or should not be re-searchable, good balance between that could be that the low loot places respawn stuff and high ones not.
I could write alot more but i see no sense of it, I let the other player's speak...