I've been thinking about the large scale changes that I brought about in my world that were inspired and developed from an exchange of ideas with my players.
In 1981, my players expressed a desire to play in a world that was more "traditional" and "less empty" than the one I had been running. I had been trying to base my world on a sort of minimal sword battle technology with elements of heavy social responsibility and it just wasn't working as far as my players were concerned. As such, I backed off and designed a world that was based on a series of lands encircling an inner sea, with predictable gradations in climate, social organization and more common themes of dungeons, greed, vengeance, dungeons . . . dungeons . . . yeah, that's about it.
In 1984, my players were losing interest in the combat system, particularly in the repetitive nature of the initiative roll, which as written was an annoying element that seemed to detract from the experience rather than adding to it. We had dozens of discussions about it. Seems like every time we ran we were talking or complaining about the combat system. And then the particularly brilliant Mike that I played with proposed a solution from some article he read, maybe it was the Dragon, where the defender's ability to attack was based on how successful had been the last attack against that defender. From this came the stunning rules, that we tweaked for a few months before settling on the best way for them to work. I have played my combats like this ever since.
In 1985, again the players were expressing a dissatisfaction with my world, not because they had an idea that it should conform to a traditional ideal but because the traditional ideal had grown to be boring. It just wasn't enough. Again there were round-table discussions on it, where people proposed all kinds of ways that elements of the real world could be injected into the fantasy construction to make it more "real." And then one day I was looking at a high detail map at the university (I hadn't started university yet but I was a regular visitor to their library) in something like 1:20 000 scale, and I realized that where it came to detail nothing could really beat the real world. That led to my running the real world as my campaign and throwing out any further notions of running a setting that was made entirely from scratch.
In 1986, my players were talking about the difficulties of buying and selling things for the purpose of making money from trade, like they were able to do in the Traveller campaign that I would run from time to time. Traveller had some simple but practical rules for trading, though they were easy to break if they weren't carefully managed (leading to players easily making millions of credits), and the players wanted to have something like that for D&D. This led to me realizing that the encyclopedia my parents had owned had references to things that individual places in the world created; I found a set of those encyclopedias cheap from a used bookstore in late '86 and started working on my trade system.
In 1989, the appearance of skill systems everywhere encouraged my players to ask me to do some kind of reboot on character secondary skills. That led to one bad table after another for years and years; I never did solve it for that campaign, that ended in '94, but eventually I did keep working at the problem until additional skills and an expressed desire for backgrounds in general resulted in my character background generator.
In 2004, after a long sabbatical from running players (while I worked on my world in abstentia), my players were quibbling about my world maps being difficult to relate to. Like most maps, the ones I used were big sweeps of empty space, divided only by geographic borders, rivers and topographical features. The dissatisfaction these maps produced (one couldn't call them aesthetic) led to my developing hex maps that were based on elevation, not topography. By plotting the elevation, I reasoned, the topography would be revealed one hex at a time and I'd have a grittier world. I came across fallingrain.com and began to copy the data from that site, one page at a time, for the whole world, in order to have the ability to plot my present day maps.
In 2007, the players were expressing their dissatisfaction with the amount of practical explanation associated with the various spells in the spellcaster's canon. This led to my beginning to rewrite all the spells (not my first time, but now with a lot more experience) as duotang books that my players could use, take home and study at their leisure.
In 2009, my daughter in particular expressed her desire for me to start writing down as much of my world design as I could, so that it would be available to her in the event of my death. I had started this blog by then, but given that the blog seemed to be a poor way to organize the information, I began thinking that what was needed was some kind of wiki. I had edited wikipedia more than a few times (of course!) and I had been working with large databases with the magazine I worked for in the 00s. A friend in Seattle proposed creating a wiki for me and for a while I loaded information onto the "Same Universe Wiki" - until technical issues and other difficulties ended that. It would be two years between the death of the old wiki and the creation of the new, "Tao at Wikispaces," which is now going strong with over 1,000 pages and 4 contributors besides myself. This wiki has now become central to regular discourse between the players and I, with it being modified and adjusted in game, when a ruling is made on some circumstance.
After all this . . .
Those are the major alterations that I've made with the player's encouragements. I don't include little adjustments here and there that have come up from time to time. Note how every one of them began with the players expressing their satisfaction, following by my willingness to change, usually followed by a moment of clarity in which I figure out how to change. At each stage, I tell the players about the changes I'm suggesting and ask them for their input. Do you think this will work? Does this sound like a good idea? Is there some aspect I'm missing? Do you want to include this or is that going too far? And so on.
This is what I meant in the previous post about the DM not acting alone (I hoped for a discussion on that; all I got was crickets). I mean listening and then corresponding with the players on ways to solve their problems, keep them interested, bring new ideas to the table and keep adjusting and changing the campaign given the resources and tools that arise from an increase in technology.
In every way, D&D is like the phone industry: we want to keep adding features, even if the phone works fine and the features are already interesting. There can always be more. More and more and more.