Everyone said already all the wonderful things I might have wanted to so I won't repeat sentiments.
Just one thing: instant classic! THIS is the kind of magical, mature storytelling that make the HP-fandom such a different one from many others: that had/s people more invested for several years in their chosen characters than JKR's fascinating world and (often black and white, simplicistic, illogical within her own rules) books alone can account for. This is the kind of fiction that I want to reread even beyond fandom when I have no interest to touch DH again in the future.