I've written before in this blog about how much work and pressure gets put on the GM if everybody has unrealistic expectations of an RPG campaign being a 'story', and if everybody expects the GM's role to be about providing the players with 'fun'. That way lies a madness of scripted encounters, fretting over 'plot' contrivances, and obsession with balance.
I think here that "Vancianism" has been underplayed. People talk a great deal about "Vancian magic" in early D&D, failing to realise that Vance's influence is far more to do with mood and feel than it is about mechanics. I'm currently in the process of reading The Complete Lyonesse, and something I've noticed is that, like with the Dying Earth books, the feeling of emotional detachment from the plot allows you to put the thing down for a week or more without losing momentum, or your interest. (It is this which allows me to read other books alongside it.) The pleasure of reading Vance, I think, is different to the pleasure of reading most modern novels - fantasy or otherwise. It doesn't come from a strong emotional engagement in the characters and what they are doing. It comes from the strange people and locations, the wonderful dialogue, the remarkable efficiency of style and exposition, and the clarity of his vision. It's the opposite of what we think of as a 'page-turner' - you want it to last as long as possible, and the reading actually benefits from taking place in small chunks dispersed across days or weeks, letting you digest it and ruminate over it little by little. Here, the characters, the story, and the narrative are almost secondary to the other pleasures.
In other words, where other novels require a level of emotional investment in the characters and their story, which by turn requires you to read more-or-less every day to keep up momentum and remain part of things, Vance needs almost the opposite.
This is how I feel traditional D&D works, in comparison to the mainstream of modern games. While what the characters are doing in trad D&D is, of course, a big part of what goes on at the table, it feels less like the be-all and end-all than it does as a framing device for a lot of other things - strange people, locations, monsters and ideas; puzzle-solving; lateral thinking; exercising creativity; and, frankly, laughing at the awful mishaps that befall the protagonists at every turn. Rather than being about the characters, it feels more like it is about the players, the world, and the game, with the characters being merely the framework on which it all hangs.
This has far more in common with the atmosphere in Vance than it does in just about any author working in fantasy - probably, in any genre. And this is no doubt why it all feels very un-pressured in comparison with the mainstream vision which I outlined at the start of this post. In the same way that you can dip in-and-out of Vance, because it isn't predicated on emotional investment, you can take trad D&D as it comes, without it having to be wonderfully climactic and narratively important every single session.
This also means that you can dip in and out of trad D&D very easily. You don't need to play the same characters each week - you don't even need to play the same group each week. It also means you can alternate players, West Marches and Flailsnails style, extremely easily.
Of course, this isn't limited to traditional D&D. My campaigns veer this way almost regardless of system, but there are certain other games which lend themselves to Vancian Detachment - including Call of Cthulu (the mood is more important than the PCs, who are disposable and who go mad or get eaten by Shub-Niggurath almost constantly), Warhammer Fantasy Roleplay (ditto), and Rolemaster (roll dice, consult table, see how many arms your PC loses in the round). I wonder if it's any accident that these are probably still among the most popular systems being used today.