It seems to me that the main attraction of D&D is that it's a creative hobby. You make your characters and worlds, and you play with them.
Shrug - I would never put it that way. D&D isn't a hobby (and neither is Warhammer - that's just marketing BS) - the
hobby is called "roleplaying", and it's quite diverse.
If you're talking about D&D relative to other rpgs, the main attraction is that a significant number of people have actually heard of it.
That strikes me as like saying "motor racing is Formula 1, because most people have heard of the Formula 1 Grands Prix". Just because LMP, world rally championship and a host of other great competitions aren't as highly hyped doesn't make them any less a part of "motor racing".
Yes, D&D gets the media attention. No, that does not make it "special" in any way other than that it gets media attention.
I'm not sure how you're defining "D&D-ness", but in my mind most of the things that are "distinctively D&D" range from quaint and kitschy to aversive and offensive. Definitely don't see any attraction to dungeon crawls, hour long combats with boards full of miniatures, sexist art, goofy large swords, Vancian magic, experience, levels, hit points, classes, or most of the "distinctively D&D" elements.
With the probable exception of the long combats and sexist art (which is found in all sorts of stuff, roleplaying and other), yes, that's included in what I'm talking about.
It's the specific take on fantasy adventuring - killing things and taking their stuff, and so on.
My thesis is (and has always) that the best thing about D&D is that it gets people to do cooperative make-believe in their spare time. Everything else about D&D could use improvement. Often lots of improvement. After all, the hobby as we know it is still in its infancy.
Again, to my ear you are talking about roleplaying, the hobby, not one specific sub-set of that that covers exactly one game line.
I don't think roleplaying needs "improvement" (which is always in the eye of the beholder, anyway) - it just needs continuing diversity. There are plenty of options already out there, but the hobby is practically infinite, so there are no limits to how much more could be done.
Skills and feats and ability scores, with one simple mechanic for action resolution (d20 vs this, compare the result to that). i.e., the good stuff.
Seriously? The skill system?? There are soooo many games that have systems at least as good, and then add other useful stuff for "toolbox" gaming on top of that. GURPS, Hero, Traveller, HârnMaster, Ars Magica (the skill system for which is practically the same as d20, but uses a d10 and is older!), Burning Wheel, Pendragon (very setting specific, but the skill system is good), The Riddle of Steel and even RuneQuest. For 'toolboxes' with a different focus Universalis is about as complete and extreme a 'toolkit' as you'll get!
The d20 skill system is adequate, don't get me wrong, but compared to other "toolkit" games out there it's hardly even a serious competitor as far as I can see.