This story has a host of things I love: a) a Hogwarts version of Upstairs, Downstairs, b) major characters shown from external povs, c) well-characterized OCs (Carster and his crew are delightful to read about), d) behind-the-scenes explanations, and e) Flitwick!!
So many fun touches: the whole Peeves business, for instance, is perfect -- just what I often wanted to do to him myself. And the robe-cleaning gossip.