For the record, I've not read any of the actual Dying Earth books, or even any Vance for that matter, despite pretty extensive familiarity with the material and concepts thanks to a lifetime of ttrpgs. I'm sure that influences how I felt about this one to some degree, maybe if I'd read Vance's stuff first I wouldn't care for this as much as I do. Because I loved this.
Shea's Lovecraft sequel, per a review way back, fell pretty flat for me. Which left me a little apprehensive about this sequel written in someone else's world, though less so due to its reputation (including amongst such notable as Patton Oswalt). This was such a pleasantly surprising experience though.
It certainly has some of the sword and sorcery tropes, though it never feels like its really embracing that subgenre. It reminds me a little bit of some of Moorcock's work in that regard.
I think what really made the book was that it was funny, which was something I wasn't expecting. Its not poking fun at the genre, or Vance's setting, but it also never feels like its taking itself too seriously. The series of misadventures experienced by the characters along their titular quest seem so random, beyond their power, and the characters themselves make such amusingly silly choices at times. This is really working in someone else's world, in a genre that maybe has aged past its prime, at its absolute best.  The world also feels lived in. We're tossed random names of places, events, and creatures in the style of sword and sorcery with the expected minimal to non-existant explanation of what or why they are. However, thanks to Shea's fantastic command of everyday language and action sequences, we're *shown* enough to have what I would say is a better understanding of those things than we typically would get from the genre (what's grue or a hoon? at least we have some idea of features, habits, and temperament from a fight).