I liked how mature they both were throughout this story. How Severus had mellowed enough to come across as a strict, but caring headmaster; while Harry had become finally cautious, both as an auror and as a prospective partner.
Their dancing around one another was beautifully done and the subtlety Severus brought to their interactions was brilliantly played.
The post-related plot had me rather intrigued throughout the story and the explanation you finally offered as to why Harry could see the mail being delivered, while nobody else could, left me smiling.
I particularly enjoyed seeing Severus dance and laugh in the snow, there at the end. This was beautifully paced and lovely. I enjoyed it greatly. Thank you, very much, for my wonderful gift, mystery writer. :D