Sick in bed and hallucinating feverishly, I today raced through Bellair's The Face in the Frost, as recommended to me by the inimitable (for so many reasons) Kent. It's only about 130 pages and a jaunty and enjoyable ride. I loved it.
What surprised me most about it was how closely its world resembles the default D&D of my youth. There are wizards everywhere and they use magic in a tool-like fashion. The setting is like the renaissance in terms of the technologies available and the way society is arranged. (It feels like somewhere in the middle of the Thirty Years' War.) Taverns are like hotels. There are mirrors, grandfather clocks and high street shops. It is medieval fantasy with the trappings of modernity, just like the world presented to us in, say, the Rules Cyclopedia.
It's deeper than that, though: the Face in the Frost also reads like a hex crawl, with an adventure locale always around the next bend in the road and random encounters popping up when inconvenient. This is not just a story: it's almost a very stylised account of a campaign.
Well worth reading as a core text of the game - far more so even that Vance's works in my view. There's no surprise it's in Appendix N. It should be top of the list.