Oh, you have killed me. This was so, so incredibly beautiful and dark and twisted and utterly utterly perfect. No possible way I can do it justice! I loved this Snape, and Harry is his perfect, clueless, omnipotent foil. You never let either of them fail the least bit in being true to their character through such a long and plotty thing, and every time I doubted and they came through, I think I loved them more.
Such fabulous imagery, and such a wonderful application of magic and treachery. And the end -- I can't say how very much I loved the end.