One of my favorite reasons to watch zombie related series is to see how they present their strain of zombies, what makes them unique or terrifying... and Gakkou Gurashi gives us the idea that these zombies, albeit overpowered by their desires to consume flesh, still retain memories to some degree even after death, and it's such an interesting concept shown through Megu-nee's scribbles, the student zombies returning to school, or even those that presumably live elsewhere... Maybe it has to deal with their most powerful, impactful memory that lasts through death?
Hence why I love this show, it's so goddamn interesting... xD