After saying all that I dont think its possible to define what an RPG is anymore though as the term is too general, so maybe none of the above actually matters
I have to agree, I just don't think there's an easy way to define the RPG genre (or any game genre) in any specific way, there's just too much overlap of features between the old-school genre names.
Since I play a lot of RPGs, I can tell you some of the features that I look for when considering a game:
: The more detailed and complex the better, whether I'm creating a single character or a party of characters. I like choosing attributes, stats, skills, abilities, careers, or personality quirks that help define my character(s).
2-Character Advancement (leveling up):
There should be some form of leveling up, and again, the more detailed the better. Leveling up your character(s) should be fun and allow you to choose new stats and/or abilities.
Whether a game is open world or map based, I love the sense of the unknown when exploring new areas, not knowing what I'll run into. I've had as much fun exploring the rectangular maps of Baldur's Gate as I did with the open world of Skyrim.
4-NPCs and/or Companions:
Indepth personalities and interactions with my character as well as the world around them. The details vary widely from game to game, with some being more static than others, but it's a feature that I always take a close look at.
5-Main Story & Quests:
Some are shallow and some are deep and meaningful, or a combination of both. Even a generic type story can work if it has decent quests. Multiple ways to complete quests/objectives that my result in different outcomes.
Weapons, armor, alchemy, food; anything that can be made. I love detailed crafting, and I'd much rather build my own super sword or gun that find or buy it.
7-Home or Settlement Building:
I love building & improving my settlements or home base throughout a game and watching it grow.
Real time, real time w/pause, or turn-based; I'm fairly open minded about that. Regardless of the mechanic, I want the combat to be fun, challenging and immersive, without being oppressive, frustrating, and overly difficult. I think it must be difficult for a game developer to create a system that appeals to everyone.
While all these are features that I look for in an RPG, none
of them really define an RPG, as many of them can be found in other game genres as well. Most of the games I play have at least some of these features, though very few have all of them. It's going to come down to an individual's perception to what makes an RPG. I still consider games like System Shock & Deus Ex as RPGs, even though they're classified (usually) as immersive sims.