Brother MacLaren
Explorer
It's like pornography -- I know it when I see it, thanks to decades of experience.Other than semantics, I have yet to see what makes certain editions D&D and certain other editions not D&D.
I would speculate that many of those of us who have a narrower view of "what is D&D" probably have a few specific game design principles that we regard as essential. For me, one of those is Vancian magic. For decades, I understood this to be a major dividing line between "D&D" and "Not D&D." In discussions with other gamers, those who liked other systems extolled the lack of Vancian magic. So that came to me to be a defining characteristic of D&D. It's absolutely fundamental to a fantasy RPG to have some way of balancing magic against mundane options. There were many ways to address this, but late 3.5 really turned me off with its movement on this issue.