So, I've encountered a problem In discussing D&D as though it's one body of work- It's not. This is, actually, obvious. Not only does every Dungeon Master run a different campaign with a different set of assumptions, but the Official D&D sources (TSR, WotC) have released a huge amount of material over the decades that features a just-as-huge level of variance. You've got your more-or-less vanilla fantasy of Greyhawk, your Tolkienian Dragonlance, your sci-fi-esque Dark Sun,all the way to the bug fuck craziness of a setting like Eberron, each of which breaks the D&D mold in interesting ways (with the exception of Greyhawk, as it more or less created the mold in the first place). Take, for instance, Halflings- in Greyhawk they are de-infringed Hobbits, roly poly pipe smokers who tend to thieving; in the D&D 4e, they're a kind of mini-warrior race; while in Dark Sun they're a feral cannibal race. Obviously, I'm going to have to be careful in how I assert my broad generalizations about this game. Because, you see, I plan on asserting quite a few.
So, let me propose a construct. Let's call it Default D&D. The basic idea is that if you were to get invited to three different games of D&D, run by three different DMs with three different groups of players, in three different decades, and not really given any information beyond that, you could make some assumptions that were reasonably likely to be true in all three games. You would probably show up to each game day ready to choose between playing Elves, Dwarves, Humans and Halflings, and then choose between magic users, fighters, thieves and clerics, with perhaps some more choices extending from there. You would expect the game to primarily feature combat in one form or another, and that you mainly be fighting some sort of non-human monsters. You would expect to be rewarded for your efforts with treasure and magical items. You would probably plan on there being goblins and giant rats and, somewhere out there, giants and dragons and evil wizards. These are all assumptions that you would probably make without thinking about it too much, and, I think this part is important, you would probably make them if you were interested in D&D but had never actually played the game before.
Consider it a sort of D&D oriented collective unconscious.
Now here's where things get a bit tricky: What would the game session itself be like? Unfortunately for my Default D&D construct, I don't think that there's a good answer that applies equally well from group to group, much less across the decades. In fact, I'd go so far as to say that, generally speaking, this is the area where the assumptions have changed to most over time . In the late 70s to mid 80s, adventures were primarily about the exploration of location. Go into the ancient dungeon and, well, see what's there (while trying not to die, of course.) At higher levels, you would go out into the Wilderness and again, see what's there. "Plots" rarely went beyond "Oh, hey, there's a totally awesome pile of treasure in this labyrinth and maybe you want to go get it?", and rarely but rarely did the world need saving.
In the late-80s to sometime just before the present day, starting with the introduction of the Dragonlance campaign setting and ending at around the time of 4th edition's release, the emphasis shifted from location exploration to "succeeding" at a Tolkienesque narrative: stop some evil guy from doing a thing so that the world doesn't end, with a thousand thousand variations upon that theme. Dragonlance seems to have offered a particularly rigid version of this narrative centric play style, even going so far as to recommend that players portray characters from the various Dragonlance novels, and that if one of the characters died they be magically brought back to life at the beginning of the next module, so as to make the over aching story "make sense".
With 4th Edition, the emphasis has shifted yet again to a sort of hybrid of the two that came before. Dungeons are entered and explored, but now the emphasis isn't so much a free form process of discovery, but rather in forging a path to the next huge set piece of a combat encounter, wherein the players get to whip out their never ending panoply of awesome powers and the plot of the game is incrementally revealed. Again, please keep in mind that I'm purposefully speaking in generalities here.
Not default D&D.For my own part, most of my play experience has been with the second Tolkienesque variety, though only rarely through published modules. This makes sense, as I "came of age" (in a D&D sense) during the early-to-mid 90s, when epic, Tolkienesque fantasy was enjoying a sort of renaissance. At the moment, I'm far more interested in the first style of exploration based play, however, and pretty much entirely averse to the combat oriented 4e style. And, as far as I'm concerned, these three emphases contain enough variation between them that they should probably be considered three different games. Still, I am going to lump them all together, or at least their trappings and general setting tropes, into my construct, and try to make it clear as to which emphasis I'm referring when it matters to whatever assertion I'm making.
So, Default D&D. Makes sense? It's a conceit, obviously, though a valid one. And it'll help later on.