Peter S. Beagle (author of The Last Unicorn) said this of Tolkien, but in a sense, I think it could be said of Pratchett as well. Except that Pratchett knew our follies, too, and used the Discworld to show us ourselves through laughter.
"He is a great enough magician to tap our most common nightmares, daydreams and twilight fancies, but he never invented them either: he found them a place to live... We are raised to honor all the wrong explorers and discoverers - thieves planting flags, murderers carrying crosses. Let us at last praise the colonizers of dreams."
I am sorry he developed Alzheimers. Once he had it, I'm not sorry he was spared the final indignities of that illness.
This was written by Neil Gaiman before Terry Pratchett's death. I don't know if it's been linked to before in this thread, but I think it says things very well.
http://www.theguardian.com/books/2014/s ... eil-gaiman