I love this so much. The unhurried pace, the scenes of Snape's post-war existence, and especially the letter excerpts, with their glimpses into both men's lives, are exquisitely done, with just enough detail to make them real, while not bogging down the story, or interfering in its slow unfolding.
Twit is adorable, and his interactions with Snape are so charming, especially when he's all offended at the presence of the delivery owl. Snape's such an interesting blend, isn't he? Such sharp-edged, sarcastic intelligence, such disdain for sentimentality, and yet such odd pockets of thoughtful tenderness. I got rather teary when Snape took his anger at the discovery of his correspondent's identity out on Twit, and I was *so* pleased when they made up again.
And Harry was perfect. I love a Harry who's had some time to grow up a little, who is demonstrably changed by his experiences, but who retains his essential sweetness and capacity for forgiveness. I'm glad he could find it in himself--despite his quite justified anger at Snape's deception--to come and apologize, and that he had the courage to reach out, to say clearly and unequivocally how much he valued the relationship they'd developed.
I also really liked the snapdragons, not just because they're a cool bit of magic (which they are), but because they seem such a perfect, unobtrusive metaphor for both Harry and Snape. Oh, and McGonagall, for whom I've always had a soft spot, particularly in her interactions with Snape, is just right.