I started GMing when the model was “roll the dice to populate your own dungeon.” In fact I remember reading the very first edition of Blackmoor, a significant part of which was a ready-to-use dungeon, and not understanding why it was there. It was so obviously “give a man a fish” when the previous material had been “teach a man to fish.” I suppose I could have studied it analytically and figured out how it had been created, but it didn’t provide any commentary to help such an analysis. And I just didn’t understand that I was actually supposed to run an adventure in this setting someone else had made up.
Looking over my Historia Ludica, I see thirteen campaigns that I ran in published game settings; eleven that I ran in adaptations of published works (one of which, Uplift, was also a published game setting); and fourteen that I ran in settings of my own creation (one of which, Worminghall, had been published not long before by Steve Jackson Games). Then there was the Toon series, which had no “setting,” being an anthology format with each session featuring two nonrecurrent settings, genres, and scenarios, the way classic Warner Brothers cartoon shows used to. Probably the oddest cases were Gods and Monsters, which was inspired by Planetary, League of Extraordinary Gentlemen, and the Wold Newton corpus, and was sort of an “adaptation” of a large part of the popular literature and film of the years from 1880 to 1945; and The Foam of Perilous Seas, which was set on the Pearl Bright Ocean of GURPS Cabal but in which almost all the geography and politics were my own inventions.
Unexplored genres? Well, when I ran Spindrift Revisited, no one had published a game for classic juvenile series like Tom Swift or Nancy Drew. Whose Woods These Are had all the PCs as real people caught up in an illusory world that was actually the size of an American small town; in fact, I had come up with a different explanation for each of the PCs for what the “real world” was like and how the false world came to be created, and which one turned out to be the truth was based on which PC woke up. Gods and Monsters grew out of my asking what genre Planetary and League of Extraordinary Gentlemen were, and Ken Hite saying that they were pulp. I suppose each of those counts as an unexplored genre in terms of what games were available then, or at least of what games I had encountered.
I really, truly don’t understand the prevalence of games or campaigns that use published adventures or campaigns. Oh, once in a while, with something exceptionally good; I was happy with Griffin Mountain, which I used for my first RuneQuest campaign, and with Midnight Circus, a World of Darkness supplement that I adapted into a scenario for my DC Heroes campaign, and I’ve offered to run Beyond the Mountains of Madness. But I don’t normally find “campaign” material as interesting as what I can come up with on an afternoon walk.