All of them except "Use rulebooks published as D&D" (especially with the OGL, we can no longer use this as a measuring stick - Mongoose's pocket handbooks are D&D 3.5th edition in everything but name, and C&C certainly has enough of D&D's cultural heritage to count as an unofficial part of the family tree) and "Dungeons as main adventure locale" (although the classical dungeon, especially the megadungeon, is very much a clear identifier of D&Dness).

A few points:
Gygaxian flavor (e.g. beholders, mind flayers, magic missiles): this is responsible for a lot of the differentiation from other FRPGs. D&D is not a generic fantasy game; it is the game with carnivorous gelatine, Giant Frogs, Tasha's Uncontrollable Hideous Laughter and Vacuous Grimoires. Although a game can be identifiably D&D by toning down the weirdness, EGG's personal stamp is very much its core element.
Hit points: hit points are required for a game to work as D&D does, but they aren't sufficient. This mechanic has been adopted by several other systems, as well as most computer games (to the extent that even platformers have them), and is one of the most successful "exports" of the D&D concept (classes are the other).
Classes + Levels (with or without multiclassing): yeah, although the precise selection of classes is finicky. Good arguments have been made both for and against having a larger number of classes and WRT various models of multiclassing. The core four are of course indispensable, others depend more on campaign flavour (e.g. a more sword&sorcery world may benefit from 1e style illusionists, while paladins would not feel right there).
Predominantly Fantasy setting: it is a "yes", but with the caveat that excursions to alternate realities, even non-fantasy, doesn't make the game non-D&D. Also, although the implied setting is very strongly imprinted by the rules, there have been successful attempts to apply D&D to slightly different ideas. Some of them worked (Dark Sun), others not so much (Planescape, and I'd include Ravenloft).

So, for those who didn't choose "main rulebooks published as D&D", are Arcana Evolved and Iron Heroes "D&D" to you? If not, why not?

Quote from: Caesar SlaadSo, for those who didn't choose "main rulebooks published as D&D", are Arcana Evolved and Iron Heroes "D&D" to you? If not, why not?

i read that answer to be "whatever who is publishing d&d says it is" as opposed to "says d&d on the cover".  so whatever 4e/5e/15e etc. turns out to be, if they don't feel like d&d to me, i wouldn't bother.

that said, i'm not sure what's in arcana evolved.  does IH have action points or the like?  that sort of mechanic is more of "fantasy heartbreaker" (thanks to whoever came up with that term) than d&d (to me).  

my answers were:
--the attributes
--dungeons
--saves
--h.p.
--classes & levels
--predom. fantasy

My other is a majority of the things on the list.  I don't think any single thing taken away, besides the name D&D, would make it not D&D.  If a bunch of them were taken away, it would no longer be D&D.

Quote from: beeberi read that answer to be "whatever who is publishing d&d says it is" as opposed to "says d&d on the cover".  so whatever 4e/5e/15e etc. turns out to be, if they don't feel like d&d to me, i wouldn't bother.

No, these are all "It must at least have X" answers - things that are necessary, but may not be sufficient.

-O

Quote from: Caesar SlaadSo, for those who didn't choose "main rulebooks published as D&D", are Arcana Evolved and Iron Heroes "D&D" to you? If not, why not?

I actually did choose the Main Rulebooks as D&D, but I wouldn't have a problem calling either one of them a D&D variant.  I ran Arcana Evolved for quite a while, and while the AE book was mostly sufficient and totally replaced the PHB, it really does require the MM and DMG for play.  Both stride the line between settings and core rules.

-O

Players.

Classes, levels, hit points, saving throws, dungeons, six stats rated 3-18, fantasy settings.  Got that?  Got D&D.

Hmmm, just the three for me. I happened to pick the three most popular ones too. Go me, or something.