I think in the beginning of the series, you were regarded as a humorous character - you were clumsy, forgetful, and very unconfident. And I think you were scared and unsure about the hat's desicion to put you in Gryffindor.
And now, 7 years later, we see that the sorting was right all along. We started to realize as the years went by, that you, Neville, were just as much a hero as Harry Potter.
I've always kind of wanted to be friends with you. At first, simply because you seemed like a sweet person, if a little bumbling. But then, I realized that you had taught me so much about self-confidence and what being a hero means. I still want to be friends with you, now because I would improve simply by being around you.
Another thing, I know if would have felt great to avenge your parents and kill Bellatrix, but then I think the satisfaction would have worn off and unease settled in. I'm glad you didn't have to kill anyone. I think it would have changed you for the worse. I'm just glad it didn't have to happen that way.
Neville, you are one of the characters I love the most. I see myself in you and what I'd like to become. And I see a wonderful friend.
Hannah is very lucky.
P.S. I'm sorry you're getting your letter a bit late. My owl, Juniper, was off hunting while I was writing and didn't come back until after midnight. But I suppose, better late than never, yeah?