I am so glad that you like the characterizations. I really worked at trying to keep some of the canon personalities, but having them change and develop because of Harry's new viewpoint and efforts.
The ending was something that I held dear. I really wanted Harry to effect serious change, not just 'rearranging the deck chairs on the Titanic.' I am ecstatic that you thought it was effective!
As for Neville and Draco, I've always thought that they had a lot more to them than was apparent from the earlier books. We saw it in DH with Neville, and I hope that it was clear that we would have seen it develop in Draco had the story continued after the vote.