I have been rereading several of the Discworld books.
They do quickly become old friends.
It dawns on me that as I read them I see specific characters- they were dim at first, but they fleshed themselves out eventually. For instance- for me, Havelock Ventnari can only be Jeremy Irons. Mustrum Ridcully can only be Theodore Roosevelt. When I read Rincewind I invariably picture a very young Gene Wilder. (No, don’t think Willy Wonka, think Leo Bloom) Eddie Deezen can only be Ponder Stibbons. Nobby Nobbs is Gilbert Gottfried. Lady Sybyl can only be Penelope Keith. And Sam Vimes is Jack Lord.
These are the faces I see when I read the book. Whose faces do you see?

When I read Pratchetts disc series, I see caricatures of people I know in his words. Accentuated, overblown….. but perfectly described.
Everyday humans I know in everyday life.
Never really flesh out stuff to an actor. I do picture the settings, but usually at distances that individual features do not stand out.
I think I might have to re-read that series again.
Paul: do you have a kindle?
Yep. Why, can you share it?
I don’t, but I never have read in that way.
Coincidentally, I’m just finishing up re-reading the entire series on the Kindle.
(Literally, I’m about 3/4 through I Shall Wear Midnight, and until Raising Steam comes out, it’s the latest.)
I don’t tend to see the characters in terms of actors, but at one point I had voices for most of the faculty of Unseen University assigned to various English comedians.
I might note – if you have netflix or such – that the BBC video production of Hogfather ( A two-part series if I recall) was well worth watching.
I see Vetinari as Lord Ribblesdale in the Sargent painting, only with dark hair. Several sizes available at this link.
http://www.wikipaintings.org/en/john-singer-sargent/lord-ribblesdale-1902
Sigvald, you must have missed Snuff which came out two years ago… Sam Vimes is on the case, and yet another race on Discworld joins the City Watch.