Your opening sequence is great. It made me want to know what was going on, and I could already tell there was going to be some interesting magical theory involved. Fabulous hook.
And the magical theory and the intricacies of the story really are fantastic, but it's the characterizations and subtle interactions between the characters that truly carry it. You've written totally believable, somewhat older and more mature Harry and Hermione; a confident, authoritative, and competent Kingsley; Severus and Lucius who've been forever affected by their experiences serving Voldemort; and a host of other characters with vivid personalities. Also, I'm dying over Goyle-who-should-have-been-a-Hufflepuff! I love the caring that develops between all of these characters over the course of this story. Very well orchestrated!