I was just wondering some peoples thoughts on this. With so many ganres and sub-ganres of games I thought this would make a perfect topic for discussion.
Skill advancement, Orcs, feminine 16 year old heroes, or what have you.
Meant to answer this when I posted earlier in this thread, but got kinda busy. My apologies.
Skill advancement, classes, etc, are game mechanics. You can find skill advancement in action titles, and classes in RTS games. What makes an RPG is right there, in the acronym: a Role-Playing Game. You play a role--not a disguise for yourself, but a role, within a social context; so it's about interaction. It can be (and often is) interaction involving combat, but it doesn't need to be. The more interesting and varied the kinds of interactions and the quality of each, the better the RPG.
That's why I rate Ultima VI and VII so highly, since you could take hundreds of different objects from within the environment and use them in one way or another. They offer a level of interaction between the physical environment and the player that has remained unmatched ever since (though Anito, Divine Divinity and Beyond Divinity have deliberately emulated it). Garriott tried to improve upon this every way he could, so that in part 2 of Ultima VII a city dramatically changes between your visits, due to an invasion; while one merchant in another town, hearing that you've helped his cousin, gives you a one-week discount on all his merchandise. In other words, the society gives the appearance of being dynamically affected by both your actions, and actions entirely outside your control. Your "role" feels more real, because it hasn't been reduced to a static
buy new weapon
kill new baddie
In another way, BG2 offered this level of interaction, but it was as a participant in, and spectator to, conversations with computer-driven party members. Where Origin Systems carefully devised a gameworld you could affect in ways no other RPG has, Bioware's writers brought to life computerized personalities. I think only one other title has matched this: Planescape: Torment. The computer-driven characters don't interact, but your conversations with them have great depth.
By contrast, a game like Diablo isn't an RPG because it isn't about interaction, it's simply about the hamster wheel of actions I outlined, above. It is an action title and a dungeon crawl, which was the subject of a remarkably expensive advertising campaign to convince a younger audience that it was something it wasn't: an RPG. The only thing that Diablo and its clones have in common with RPGs are a few game mechanics, like player stats, spellcasting, etc. But many of the same stuff shows up in RTS titles and even turn-based strategy titles. This doesn't make them RPGs. You could even have an RPG without player stats. I've seen and tried one, Procedural Arts' Facade, that puts you in a situation of dealing with a couple (as a friend of the family) whose marriage is completely on the rocks. No upgrades, no skills, no stats: just hardcore roleplaying, ferreting out details of the really painful damage two people have been doing to one another attempting to help matters, while they try to keep up the pathetic facade of a friendly night over for dinner.
Note, I'm not saying an RPG has to be without combat. My point is simply this: a role-playing game is by definition all about playing a role in relation to an Other--whether one computerized person, a large, complex setting, a society at large, or all three. Anything added to the mix may work or may not, but it isn't part of what defines the genre.