Aqua Vitae said:
For me?
It's not D&D.
Must I accept it as such because cunning capitalists claim it is?
No, you don't have to accept it as such. Everyone has his own definition of what's D&D, based on his experience with the game.
As long as you don't try to insult someone with your claim, and only state what it means for you, there should be no problems. (That won't help if someone wants to have a problem with you, but nothing helps you against that.)
For me, what is different or unique:
The MATH. I look at the different classes. I look at the monsters. I look at the guidelines. And I see a system that I can "mathematically" understand. I see the design behind.
In every other game I've played, the math typically looked very "hand-wavy". It kinda works. It is sometimes a little off. No, there isn't a real system behind it. Most systems have game-breaker abilities that don't fit into the framework, and often are broken or seriously impact (usually negative) the game.
Game comparisons (Shadowrun and D&D 3E, the systems I am most familiar with)
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Shadowruns worst aspect - in my mind - was always the Initiative system. How do you balance extra actions per round? How can you create a fair balance between the reflex-boosted street sam and a unboosted Decker? (Well, the answer is, you can't. You're not even supposed to. But just because the system works as intended doesn't make it good). The (combat) magic system, too - you can use your combat pool against firearms (3E, in 4E you use the Dodge skill), but against spells, you only get the little bit of Willpower you have, while the mage uses his skill and his mage pool (or ability + skill in 4E)?
3E Shadowrun also still suffered from a dice system that broke down even in an average combat system, making success or failure changes unpredictably.
D&D 3E system gave me formulas to arrive at numbers describing a PC or a monster. What it didn't give me was to say how strong it was in comparison with another PC or monster. It did give me damage caps by spell level and magic type (arcane or divine), but it didn't tell me anything about secondary effects, range, area and stuff like that.
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If I am looking at 4E, I can see the math behind it, how it works. Sure, it's not 100 % (
hmm, should this effect Daze or is Stun okay, too?). But all DCs, Defenses, attack bonus, skill checks, I can compare them and see how they interact.
And yet, the surprising thing is - it still does the oddball stuff I learned to appreciate in D&D - spells (and powers) with unusual effects - bigby's hand, mirror image, mordekainens magnificient mansion.
The only system that I'd be willing to give the credit for a similar well-thought out system (but entirely different looking in execution) might be Torg, but I know that that game definitely had some short-comings. (Glass-Jaw Ninjas. Anyone with a high Dodge has a hard time to survive a hit, since you roll to-hit and damage with a single die, and the bonus result is applied to both... If you hit a Ninja, it's always a head-shot, so to speak.

Well, maybe 4E will show us its Glass-Jaw Ninjas soon, too. )