Honestly, I reread the manga not long ago and was struck by how much denser the narrative feels compared to the anime. The character development for minor figures like the history teacher, Shizuka, gets more panel time, making the school's collapse feel more personal and chaotic. There's a subplot about the student council's initial, failed attempt to maintain order that the anime completely glosses over, which adds a layer of tragic bureaucracy to the early chaos.
Visually, the anime amplifies the... let's call them 'fan service' moments to an almost comical degree, often pausing the zombie action for extended sequences. The manga has those elements too, but they're woven into the panels more fluidly, feeling less like deliberate pauses. The ending is the biggest divergence, of course; the manga stops abruptly due to the author's passing, while the anime concludes on a slightly more hopeful, if open-ended, note at the shopping mall. I find the manga's raw, unfinished state has a grim authenticity the polished anime lacks.