It need a Dungeon Master.
Only D&D can and should.
Mechanics changes, the Gygax & Arneson game was more a platform' concept in my eyes than a well rounded game, and no game colud be perfect. It has to change, to refine, to appeal different generations.
But it needs basics concepts carved in. Like a Dungeon Masters building a story with players. I can't think to other foundamentals.
Levels? Maybe, maybe not, its just a mechanics, it can change.
The six stats, alignment, classes, specific races, all the same with levels.
Magic? Definitely not!
The only thing i will miss in a D&D game that's totally arbitrary are dice, i love dice.