Couple things that I value in RPGs:
1) versimilitude
Writing in games generally serves to give context and spice up quests and systems. A good writing in games will contextulise "gamey" elements and make them feel natural. It also applies to how character behave, what they ask of us, and how they respond to our actions, cohesion between written text and enviroment storytelling. In a game that is "well written" I expect to not run into a problem of "this doesn't make sense, but that's how game works". This is, of course, not as simple as "good writing" and more of a cohesion between game's various elements. I would point to Supergiant games as an example of studio who is really good in contextulising their designs - even stuff like difficulty modifiers have in-game explanation and acknowladgement. Player's can make game more difficult for themselves for fun, but also have narrative reason to do so.
2) Worldbuilding
In RPGs we tend to explore fictional settings, and are asked to engage with characters who inhabit it, and often make decisions that will impact the characters, I find it important for the game to paint a believable, and engaging setting - a place about which fate we will carry, and where we would be able to understand and contemplate impact of our actions. It includes communicating to the player how the world works and also writing characters so they behave in the way consistant with the world they inhabit. Quests would ideally be part of worldbuilding - if we are tasked to do something, it should feel like we interact with the setting we are in, rather than doing unrelated stuff. Even doing a fetch quest can feel meaningful, if it feels like people who ask for it need us to help.
Having worldbuilding, doesn't mean overwhelming amount of codex entries or lore books. While those can be handy to add additional info for those who want it, the game's plot, character's motivations, and context should be included in game proper.
3) compelling protagonist
Whenever a game has custom or pre-defined protagonist, that protagonist must be memorable and expressive. In case of pre-defined protagonist it means making sure that the game and the player are on the same page as to who the character is, and how much (or little) impact player can have on who the character is. If we play as a pre-made character, player shouldn't be able to do what the character wouldn't do. Even in case of custom protagonist, it is perfectly fine for developer to set up boundries (it is even necessary to do so, due to game's content and reactivity being inherintly limited).
If the playable protagonist is custom he or she still needs to have personality - that personality might be up to the player to pick, but it should be there. In other words, rather then remaining blank through the entirety of the game protagonist personality should be shaped by player's actions and decisions.
In short:
Good pre-defined protagonist: a character who is predesigned by devs and players have access to choices that make sense for that character
Good custom protagonist: a character whose character and ideology gets defined as player plays the game and makes choices
If pre-defined protagonist doesn't mesh with game content, or we never get to define or express character in game than those are poor protagonists
4) narratively interesting choices
A choice in an RPG is compelling if there is a narrative weight to it. A moral challenge for our character to solve, a decision about ideology to make, a side to pick. Ideally each major decision should reveal something about our character as well - examine his or her values. Ideally desisions should be varied as well - games that follow predetermined paths (good vs bad, paragon vs renegade) just aren't terribly interesting as players really make only once decision, and just continue reinforcing it throughout the game. Making multiple, independend smaller decisions is just more interesting that few major ones.
If player is being asked of something, their knowledge should be on the same level as the characters - if we get asked about something that the character would know, but the player wasn't provided with necessary information than that's a poorly implemented choice.
This exactly. Both very simple and immensely complex.
Per what I've seen so far, I feel BG3 misses the mark. Then again, I don't think the narrative was ever one of Larian's main focuses.