Re-re-rereading Discworld for my nightly read. I understand there's some debate within the fandom about when exactly the series "grew the beard", but the textual differences between The Colour of Magic and The Light Fantastic are pretty stark. It's definitely a step on the path.
@tryst I was listening to sort of an "audience with Terry Pratchett" thing on iplayer and he said that Mort was the first book he was "really pleased about" and the first two books are "jokes at the expense of Fantasy; the plot is there to stop the front and back of the book banging together in the middle"
https://www.bbc.co.uk/sounds/play/p00fc3w5
Bookclub - Terry Pratchett - BBC Sounds
BBC