Oh my. Wow. I have the hugest lump in my throat from that ending. Utterly, painfully perfect.
I love the pacing of the story, how different parts were revealed only when they became necessary not purely exposition.
I love how you dealt with the agoraphobic reaction, the little quirks Harry and Snape developed and I really like the character of the castle (although I thought for a second the form was going to be a dragon).
I so much (as I hope you can tell), particularly Harry and Snape's characterisations which are removed from canon in a way that it is clear how they got from one place to the other.