I love how the people and the language change; how Snape isn't really static. The way you've tied up the loose ends from the end of the series is remarkable--painful too--but just right.
The one thing that really got in the way of my enjoying this story was the number of spelling and grammatical errors. I know that festival fics are sometimes beta'd on the fly, but something small showed up every couple of pages, and that was rather annoying.
Do yourself a favor: get someone to go over this with a fine-tooth comb before you post it to archive or to your own journal.