Here are my thoughts after the first wave of comments. You can read the original OP below.
The name of a genre should describe the gameplay as accurately as possible and convenient. The core gameplay element.
Allow me to repeat:
In strategy games you have to employ strategic thinking skills to win.
In racing games you need to race to win.
In shooters you have to shoot things to win.
In platformers you have to maneuver platforms to win.
In beat'em'ups you have to beat them up to win.
Simple and elegant. I agree that there are misnomers, like the adventure genre mentioned by Couscous, but I wanted to focus on RPG.
Then why is RPG such a difficult term? The name implies, after all, that you simply have to role-play to win.
What is role playing in general?
Basing on the simple example of an actor playing a role, we can easily say that playing a role means acting according to your character.
Khavall suggests that we have to employ a definition specific to the discussed subject, however.
I agree. After all you play a role of Master Chief in Halo, yet it is a shooter. You play a role of Garret the Master Thief in Thief, yet it is a sneaker. In Race Driver: GRID you play the role of a race driver, yet it is a racing game. Why? Because the CORE GAMEPLAY element in those games is, respectively, shooting, sneaking and racing.
Why isn't Diablo a role-playing game? Because the only role you can assume in this game is that of a fighter (no matter the tools he employs to fight, be it melee, bows or magic), the only thing you can do in this game is fight (traditionally, we call such games hack'n'slash). You have to FIGHT to win the game.
Why isn't Oblivion a role-playing game? Because -despite the fact that you can assume various roles in it, you can be a diplomat or a thief- the vast majority of the gameplay is still combat (even the thieves' guild quest involve mainly combat, especially in the latter part of the questline). You have to FIGHT to win the game. There probably are situations where combat is possible but not necessary- but it's the majority of the gameplay that describes the game, not separate situations.
Why aren't JRPGs role-playing games? Because, despite the fact that you take part in a story (and it can be a very good story), the only part of the game that actually requires player input is COMBAT- therefore COMBAT is the core gameplay element. You have to FIGHT to win the game.
Why is Fallout a role-playing game? Hmmmm...
Is it a shooter? No. A vast majority of situations can be handled without combat. Is it a diplomacy game? No- despite many possible diplomatic options, you can solve most situations through properly applied violence. Is it a sneaker? No, there are a few sneaky missions but they're neither prominent nor required to win.
So what do you have to do to win Fallout? You have to PLAY YOUR ROLE. YOU HAVE TO ACT ACCORDING TO THE NATURE OF YOUR CHARACTER(S). Same for Arcanum. Same for Planescape:Torment.
If there were a more specific way to describe the gameplay, it would define the genre. Of course, you could call it a fighting/sneaking/diplomacy game, but that would only be true if ALL of those elements AT ONCE were required to win.
If you are forced into a role and you don't get to change it (Halo, Thief), it's the role that defines the genre of the game. If you get choice- it is a role-playing game. If you get multiple choices but only one possile outcome- then it is a very poorly done role-playing game.
Somebody mentioned RPGs without stats. I gave it some thought and yes- it is possible. If role-playing means "acting accordingly to the nature of your character(s) we should take a closer look at what can define that nature.
-Likes and dislikes
As you can see, at least one of them (past deeds) can be defined without stats. My dream RPG would employ all those elements for both the PC and NPCs (in fact, I'm preparing a detailed devplan for such a game and I'm planning to make it).
I have no good way of starting this thread, so let's get to business immediately.
I wanted to discuss the notorious "what is an RPG
?" question. I'll start by posting some elements of MY definition and some things I consider common misconceptions and then I'd like to hear your opinions.
I only have one request.
If you think some gameplay element is a core RPG element or you are sure that a certain game IS an RPG, please explain and post arguments. We don't need posts like "what, Xxxzzyzx is surely and RPG, gtfo!".
Before we get to the "G" part, let's define ROLE-PLAYING, as even this seems to be a misunderstood topic.
Some people think roleplaying is simply acting according to a certain theme, behaving consistently (even if it is consistency in inconsistency) or realistically, no matter what. Well, no. Let's take a look at what it looks like: UESP wiki on "roleplaying".
That, my friends, is what we call cLARPING. Running around a house and breaking furniture in a cRPG isn't role-playing an asshole unless the NPC is programmed to react negatively to such behaviour. Stealing a guard armour and walking around the town isn't role-playing a guard unless you actually get to join a guard faction and patrol according to game mechanics. Otherwise you might as well turn off the PC and imagine those things yourself. (alternatively, you could be cLARPING in other games! Hey, I'm playing Need for Speed but I'm "role-playing" a kid who got the car from his dad and so I can't so much as scratch it!)
So, in order for a game to be a cRPG, the game mechanics must support the role-playing. How is that done? Well, in traditional RPGs, it is handled by the game-master with help from the game ruleset. In a cRPG, it's all about the rules. Sure, some games might have RPG elements but we can recognize an RPG game by the fact that the main focus is on designing and executing those rules.
What rules can they be?
While it's not necessary, a good game should give you a choice on how you want to handle the problem before you. Usually that means combat (be it melle, ranged or magical), stealth (be it assasination or sneaking) and diplomacy (persuasion, intimidation and bribing). If we are playing an adventure game, there is usually just one solution. In an RPG, you are presented with choices, and your task as the player is to choose the one option that best fits your character.
Well, what meaning has a choice without consequences? We all know Bioware's tricks, where you are presented with multiple dialogue options that (almost)always boil down to the same result. There's also fake choice (you can join the Fighter's guild or you can ignore it! Choice!) of course, but that's much easier to spot. If your choices (be it the choice of the PC you've built at the start or the choice of your behaviour and actions) triggers an appropriate response from the game world, you know you're on the right track to a good RPG.
One of the most important elements is basing on the PC (player character) skills and attributes to determine your options and success chance. Sure, the player skill can also be involved but if it's all there is to it, we're dealing with an action game (like Quake), a stealth game (like Thief) or a diplomacy game (haven't played one, sadly). So if you've invested character points in combat, you won't go sneaking around the castle because your lack of skill and loud chainmail will quickly have you spotted. If you've treated INT and CHA as dump stats, you will have few dialogue options and even those you get will have a lesser chance of success (ever played Fallout with INT=3?).
While character development and gaining new experiences MIGHT be an interesting gameplay element, it is by no means necessary. The jRPG crowd used to monotonous grinding will probably be shattered by this realization but let's face it- you can very well play a role based simply on the stats you've chosen at the beginning of the game. IF, however, you start with a pre-defined character (and have no option of modifying it initially), there'd better be some character development, otherwise it's not much different from games like Quake and Thief- those DID have stats after all (albeit hidden from the player).
Quite the opposite: the way the story develops should also be based on the role you've chosen and how well are you playing it. If there is only one path to follow, which consists of anavoidable plot points, we're dealing with a story-driven game- something like reading a book in which YOU get to choose the words used, but the story stays the same. While a good story is always welcome, in an RPG it will only be a background for what is going on. Some counterexamples are Oblivion (where every quest has just one solution), the Witcher (at the end of Chapter 1 you're thrown into prison no matter what). Again, the games coming to mind might feature RPG elements, but the main focus of the game is what counts.
VISUAL CHARACTER CUSTOMIZATION: just... no. What the hell, where did you get this idea!?
So, what to do with all those games that don't fall into the RPG category? Well, when I was a kid we used to call them by various names.
Dungeon crawler (Might and Magic, Dungeon Master)
Action-adventure (Ultima, Witcher?)
Hack and Slash (Diablo, Oblivion, Nethack (I do believe roguelike is a term regarding presentation rather than gameplay)
I'm interested in your opinion. Just please try to look at this subject with a bit of reserve and scepticism. I know some are prone to getting carried away when discussing it. OP prone to revisions.
TL;DR - some people have weird ideas about what a cRPG is.