The voice. The narrator immediately brought me into wartime England, and not only that, but into Toby's head, with his idiom and accent intact.
The place names! Wallop, Pinchley, Piddleby... so much in keeping with Rowling's place names, and also evocative of the entire social milieu in which Toby is placed.
I enjoyed how we got to see the magical creatures, spells, and Muggle-repelling charm from Toby's point of view, without being told what they were.
I wonder if you did a lot of research to get the era right. The music, fashions, cars, technology ... It certainly all sounds authentic to me!
All the old wizards wanting to marry Eileen was so funny! Especially the one who'd lost 4 wives and was 'only 86 and ready to move on from his heartbreak', lol.
It's wonderful how strong Eileen was, and how she was able to break away from her overbearing family.
The ending does leave me wondering, though, what happened in the ensuing years, after Severus was born, to lead to his apparently difficult childhood and home life.
Still, this was a great story and I enjoyed it very much. :)