I adored this! It satisfied a lot of fanfic itches I didn't realize I had.
1) that young Snape, however much you love him, would be rah-ther a trial to deal with. I loved the way he imprinted on Draco for a while.
2) In umpty-thousand fanfics over the last few years, I don't remember anyone going so deeply into JKR's internal Harry-voice so well and sustaining it for an entire long story like this. The way he tries to reason things out, the way he reacts to people -- it's pitch-perfect. I LOVE the DADA duel -- it's exactly right for the next step after Harry's smart remarks in HBP.
3) I love that you made Snape old again! My heart broke for him when it happened, but this way is better. The thing with most de-aged Snape fics, and I love several of them, is that the Snape who gets rewarded in them isn't *our* Snape. To see the prickly bastard grope HIS way to a happy ending without sacrificing his essential character was really fulfilling.
The only thing I might have wished for is a little more acknowledgment of the grief everyone in the school must be experiencing (a casual mention of Crabbe and Goyle brought me up short.) But then, that wouldn't really have fit the tone of this story, which fits beautifully with everything else in the series rather than the angst of the end of DH.