Glyfair said:
How constrained do you find yourself in your own campaign world? Do you feel that you have to leave the major players of Hell the same as mentioned in TSR/WotC publications? Do you feel you need to use the Great Wheel cosmology in your campaign? What other elements of D&D canon you feel tied to?
Why do you feel constrained? Is it your own choice, or do you feel your players would expect it?
I can run a canon D&D adventure, but it will often be filled with various minor house rules. By minor I mean things such as suggested class and level demographics (most are Experts 3-5 rather than Commoner 1, and the Expert class gets (non combat, non magic) bonus feats at first and every fifth level). I might also use a few rules from the UA, feats, etc from various non-core books (the Complete series - on a case by case basis, various others - and occasionally a third party book).
I guess it would work out to about 90-95% core canon.
Settings, however, are another matter entirely. I completely ignore suggested cosmologies and come up with my own. If I run a game in a major setting, I consider the campaign setting book the only history book available, ignoring published novels and adventures that I do not have and have not read. Rather like two directors could have (and thus produce) very different versions of Hamlet, so too might I end up using a characterization for a known NPC that differs from what is strictly canon - perhaps a little, perhaps a lot, based on my own views of the being in question.
So I suppose you could say that when I run a 'canon' game it tends to be mostly canon in rules and canon in setting on a very much case by case basis.
However, I feel it necessary to point out that most of my games are not 'canon' games (ie: they are not even attempting to be canon, although I run such from time to time when the group may feel interested in such - usually between major adventures / campaigns). Most of them use unique settings, significant numbers of house rules, a completely different magic system (usually EoM,R or EoM,ME or a variant thereof), and various alterations to the creatures (especially undead, constructs, animals, and fae). I also, in most of my games, tend to include third party options that - collectively - tend to really alter the feel of the game.
So my typical games are about as non-canon as you can get while still remaining firmly d20 in nature (just not all that much D&D).
When I run a 'canon' game it is important to me, but only when I run such a game. Elsewise it is just like so much else of the rules and game setup: suggestions to be considered and used as needed / desired or ignored.