Honestly, a lot of the recommendations you see in these threads circle back to the same few modern titles, but I think the real champions of world-building in this mash-up are actually some older, slower-paced series. They had the page count to really dig into how society rebuilds after the cataclysm, not just fight monsters. Take Kate Elliott's 'Crossroads' trilogy, starting with 'Spirit Gate'. It's not your typical ruined-Earth apocalypse, but a fantasy world where the ancient, world-spanning roads are breaking down and the guardians are gone. The world-building is in the societal collapse and the regional cultures trying to fill the power vacuum. You get intricate politics, trade routes failing, and different belief systems clashing, all stemming from that foundational magical disaster. It's less about scavenging for canned goods and more about the long, slow unraveling of an entire civilization's infrastructure.
Another one that doesn't get enough love is Sean Stewart's 'Galveston'. It's a quieter, more literary take. The apocalypse here was a slow creep of magic back into our world, and the story is set decades later on a flooded, haunted island off the Texas coast. The world-building is incredibly atmospheric—it's in the way old Mardi Gras traditions have morphed into something new for survival, how families wield magical 'luck' as a currency, and how the ghosts of the past are literal, persistent forces. The strength isn't in epic battles, but in how every custom, relationship, and bit of dialogue feels shaped by this profoundly changed reality. It builds its world through mood and cultural detail rather than exposition, which I find way more immersive.