Honestly this is a difficult problem in game writing. I did a talk about this a while back... I arbitrarily divided game protagonists into a bunch of categories along an axis from "less strongly characterised" to "more strongly characterised":
- Blank slate - e.g. Icewind Dale
- Faux blank slate - e.g. Gordon Freeman, Doom Slayer
- Extreme choice - e.g. Torment, Disco Elysium
- Limited choice - e.g. Commander Shepard
- Defined but flexible character - e.g. Geralt
- Defined character - e.g. Joel (The Last of Us)
- Runescape is anywhere from Blank Slate to Limited Choice depending on the writer and period. In general, the player is not a "character" - they do not have any beliefs or needs.
The reason I say it's difficult is just that different players have different preferences. Some players much prefer something like Bayonetta where you have a strongly defined character who makes decisions and who you watch kinda like a TV show. These characters are likely to talk a lot and volunteer a lot of opinions. Other players find this highly unimmersive, and want to "roleplay" (not necessary in a formal sense, just immerse themselves in the situation a bit) either as "them" or as some character they've imagined, a la something like Skyrim.
I don't think "depth" is the right term for what you're describing, but I would definitely agree with "characterful" although it's highly dependent on the author. In some old quests the player is very strongly characterised (typically as a wisecracking buffoon who witlessly aids the villain) and in others they barely say anything.
For a lot of the sixth age content we made the conscious decision to have the player be less uh... stupid, essentially, but we do still get regular complaints from quest players that the player should be smarter than they are.
Mod Zura (who wrote Daughter of Chaos and the civil war miniquests, and will be writing the first major quest of 2023) is quite keen on allowing more player choice in dialogue, and one of the options he wants to allow more often is a more sarcastic, humorous option. In theory this allows for the best of both worlds, because the players who want to be stoic and sensible can choose to be, and the players who want to be wisecracking buffoons can also choose to be. I think it'll take some experimentation to find the right amount of choice - I couldn't personally see us at the Fallout 4 level of "every player line is a choice" (and I'd note that Fallout 4 executes that extremely badly) but we can probably go much further than we have in the past.
That said it's unlikely that we'd repeat plot points along the line of "the player makes a stupid decision which is the cause of the plot in the first place" because that's not really something we can let the player choose to do or not.
At a personal level I actually prefer to write more strongly characterised player characters. I like to use the player to volunteer information rather than just ask for it, and I like them to express opinions where possible. In my own writing I do that a lot more than I would on RS, because in a very real sense the RS PC isn't "mine" to write for. I'm also generally more about lore than character, so it tends to be quite lore focused as in this exchange from Azzanadra's Quest:
https://runescape.wiki/w/Transcript:Azzanadra%27s_Quest#Wen's_egg
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