Wow, that was excellent! I adored the 'what if' scenario (one detail changed, really, and a totally different if not unrecognisable world), especially the way it kept the reader in the dark about what is real for a long time - very effective. And I loved how essentially canonical it was despite the AU bit :). Portrait!Dumbledore was gorgeous, and the way the 'castle' is speaking to Harry (and most of all the explanation for it, as Harry's own suppressed memories - it takes up how much Hogwarts as a refuge means to Harry in canon).
I liked this Harry immensely (he feels younger and more likeable than canonical Harry in spite of the horrible experiences he's had to make as Voldemort's pet - it felt as if he's been drawing on all his strengths and turn him into, well, 'condensed' Harry in a way that makes all his positive character traits shine. Dunno if that makes sense, but I loved him!
And Snape is wonderful - a touch softer, well, at least Harry's fate has taken care of the 'Harry-hating' elements of Snape's personality, and still gruff and not quite kind - although his kindness when he sleeps with Harry was quite something.
And of course my inner Lucius-lover squeed madly at Lucius's very canonical cameo at the end. I also liked that the story ends without the war being won - although the final meeting of Snape and Harry was gorgeous, and the Patronus-ending worked very well.