Part of the reason I like D&D, maybe the main reason I like D&D, is I think it does a good job of letting us all sit down and play together. This is I think the result of having been invented bottom up through the course of play in an organic fashion. It's not the product of ivory tower theory about what would be fun, but the product of years of adopting rules, throwing rules out, and settling on something that seemed fun.
It took me a long time in my RPG career to realize how essential that was. It's hard not to have all these bright ideas about how much better everything would be if it was only more realistic, more elegant, more flexible, more like this sort of fiction, and so forth, but when you actually play your bright ideas you find that well, in practice they aren't maybe as great as you'd thought that they'd be. I use to take it for granted that D&D was only good because of nostalgia or because everyone had played it. It took me a long time to humble myself enough to stop and try to figure out what was right with it instead of just what was wrong with it. When I did actually turn my thought to what was right about it, it was like a revelation. I haven't ever looked at game rules the same way since.