Given that the post-apocalyptic train has been passing by us for some time now as we wait at the crossing, the element I would be looking for is the reason for the telling of the story. Even the most burnt trope can be made enjoyable if it has a backbone, a purpose that goes deeper than the props of the trope. There's surface story and there's deep story. There's skin and there's meat. What's the meat? You don't have to answer that - it's rhetorical - but that's the element I would be looking for in such a story.