Look, I'm gonna cut straight to it: 'The Stand' by Stephen King. Everyone will probably say that, but there's a reason. It's not just the virus and the good vs. evil showdown. It's the hundreds of pages where people are just... lost. Walking empty highways, hearing echoes in empty houses, trying to remember what a grocery store felt like. The action is in the survival, the scuffles, but the emotional gut-punch is in the loneliness and the weird, fragile communities that form after.
I always think about Nick Andros, the deaf-mute drifter. His whole arc is about being unable to communicate in a world that's lost all its noise, and how he becomes vital precisely because he listens differently. The big battles are almost secondary to those quiet moments of human connection, or the lack of them. It's a brick of a book, but you feel every mile of that journey.