1) Have persistent character progression with player-exposed stats.
2) Combat had to feature prominently
3) Combat resolution for a standard playthrough had to be determined in large part due to the skill or your character and not player skill.
4) Player choice and consequence, either in story or character development/building.
5) It had to have an actual narrative (stripping purely systems-driven roguelikes from contention).
6) Some element of exploring a world or virtual space.
Finally, someone offers a list criteria, which should be the only part of a list that's worth discussing. The criteria should tell us about what you value and the weight you give various elements. In this case, you 6 points aren't a criteria for what makes a good RPG, but simply what makes an RPG.
Thanks for taking the time to go the extra mile.
Many have struggled with video game terms, language, and categories. Many attempt to use terms, but they end up triggering the neologist in me. ("mechanic" is my biggest trigger word) It's especially hard to develop a clear language just before you need to put it to the test (like when making a top 100 list).
These 6 points are a decent start, but the whole list has a few holes. This is not to mention that the criteria wasn't applied thoroughly to the items on the list. Here's how I see it.
1) Have persistent character progression with player-exposed stats.
Persistent character progression and player exposed stats are not essential to RPGs. Perhaps a better way to explain it is that this point and the rest of the 6 don't seem to articulate the aesthetic end user experience that RPG strive to create. It doesn't reflect why features like stats are so widespread in the genre.
In essence, RPGs are a type of game that simulates and abstracts rather than models via systemic interactions. So RPGs commonly strive to create a world rich in conceptual detail, details that are particularly hard to model via rules. So we have abstractions and other systems to roughly bridge the gap. This way we can express the idea of a character getting strong over time via exp and leveling. And we can also create a stat for just about anything from digestion (The World Ends With You) to Charm (Persona 5) to Stache (Mario & Luigi). While the Miyamoto/Nintendo/opposite way to create a game controls/fun first with the level design and wrinkles developed afterward, RPGs, from what I gather, start with the bigger concepts (story, world, etc.) and then create systems to convey these ideas.
Knowing this, you can have an RPG with no exp. You can have the character never level up and instead focus on gear/weapons/anything else. And you don't have to have the stats exposed either. Being nerdier than most, we gamers love our numbers though so it's no wonder RPGs use them so much.
2) Combat had to feature prominently
Likewise, combat isn't a requirement. Think of it this way, if you can understand that various turn based, stats/numbers driven scenarios are in fact simulating combat encounters, then you can imagine that just about any action can be simulated in a similar way. In the same way that anime can give the ol' anime treatment to anything from Ninjas (Naruto) to baking (Yakitate Japan), the "combat" part of an RPG can be anything from non-violent "arguing" to cooking (does Battle Chef Brigade count here?). All in all, most RPGs (and games) have some kind of combat/battle gameplay because conflict and fantasy combat world are popular.
3) Combat resolution for a standard playthrough had to be determined in large part due to the skill or your character and not player skill.
This one is complex. The vagueness of this point stems from the "in large part". Is this 30%? 51+%? Regardless of how simple the basic "attack-attack-heal" RPG strategy is, playing RPGs is still a skill-based activity. You have to know how all the moves function and execute at the right time unless your characters are ridiculously over-leveled. I assume we're talking about normal playthroughs so we don't have to worry so much about considering the extremes of over/under-leveled gameplay.
So, RPGs are skilled based even if the whole "avatar" skill thing complicates our assessment. And certainly, Action games and Action-RPGs bend the skill spectrum farther way from "avatar skill" being relevant. If you're trying to say that the way you invest and customize your character should matter in an RPG, I agree. I think that the decisions you make in any game should matter. And I expect the same from RPGs.
If you're trying to say that RPGs should be built in a way where leveling is a requirement to progress in some cases, then this is more of a balance concern than a genre-defining consideration. Imagine a really easy RPG with all the turn-based, stats, exp, equipment, and character progression as Chrono Trigger. For this EASY-RPG players might never have to slow down to grind due to the difficulty balance. It's still an RPG. You can test this by playing any RPG on easy mode. You might be able to win these games by indescriminately mashing the buttons on the controller. If this is possible, these games would still be RPGs, right? So does the balance between player and avatar-skill really matter?
4) Player choice and consequence, either in story or character development/building.
This point seems straightforward, but I don't think it says what we all think when we read it. By mentioning consequence, you're basically saying that the choice shouldn't be a false choice, where the game will continue forward regardless of the option you picked. This is generally a good thing for any game that gives you a seemingly weighty choice.
So maybe you're saying this choice should affect the story or the character in some way. Again, any time you customize your character (armor, weapons, skills, portioning exp, etc.) you are affecting your character development. If this is the case, this part of point #4 is mostly covered with point #1.
As for the story part, any side quest, alternate ending, or story branch should qualify. I feel that an RPG can be completely linear with its story. So if you can customize your character at all, then the story can be linear and still meet the requirements here.
5) It had to have an actual narrative (stripping purely systems-driven roguelikes from contention).
"Actual narrative" is another troublesome phrase that seems to have a bit of bias to it. It doesn't take much for a work to have a narrative. Stories and the telling of these stories can be extremely minimal and still qualify as a narrative. Most people tend to prefer complex stories to minimal or simple ones. I like all kinds of stories, so I tend to look at points like #5 differently. So it seems that most games would qualify for this one these days.
6) Some element of exploring a world or virtual space.
I think the best way to interpret this is for a game to feature non-required areas, quests, and perhaps secrets. It's not much of an exploration if the experience is linear (according to how most think of exploration). So tucking a few chests here and there or having a side quest is enough to qualify here too.
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So when it comes down to it, your 6 points are still very broad in how they apply to games. They don't do enough to separate RPGs from non-RPGs. The top 100 list makes this clear enough based on the inclusion of many titles that are commonly labeled as genres other than RPG.
After understanding the core design behind RPGs and how this core shapes their common tropes, the final trick is to understand that the RPG label works best as a sort of catch-all category. When a game features other more prominent gameplay types, it is probably best categories as another genre.
Ultimately, I would find it more interesting if you gave us a criteria for what you think is good about these games. Regardless of the fringe cases and blurred genres, articulating and weighing a criteria for what makes such a complex genre good would take some real effort.
Best of luck.