One of the things about Mass Effect that stood out the most to me was its Band of Brothers approach to party building: the fate of the galaxy took a backseat to Shepard finding exceptional, often haunted people and building them into a team that followed her for her entire adventure. Like most Bioware games I think a large part of their character came from the high quality of the writing, and from the fact that practically everything Shepard did was as a team. It's one of the few games where I made party composition decisions based on who I wanted to see more of instead of pure numerical optimality, and I happily played through the game multiple times in large part just to see how everybody's stories changed with your decisions. Writing alone, however, is insufficient: Skyrim lavished incredible amounts of attention into giving some of their NPCs large amounts of dialog and backstory (while leaving a lot of them tragically shallow), but I found that I didn't care- I've played Skyrim numerous times on different characters, and the only characters I can consistently remember are the jester from the Dark Brotherhood, because he was incredibly irritating, and the guys in funny robes who scream at you, because of how long the unskippable cutscenes with them were. My game procedurally generates a completely new cast of NPCs every time you start a new game, so I can't rely on writing alone. In its place, I think that giving the player as many opportunities as possible to map narrative into their party: build at least a rudimentary social AI that allows them to watch their party interact with others as they travel, and find distinctive but non-annoying ways for party members to assert their personality as the game progresses. This can be pretty richly done with some very rudimentary things: developing small variations on common animation libraries (movement/idle/combat/response) that conveys personality through body language, just generally give the party chances to do barely enough for the player to write their own story with what they see. What other big blocks am I missing? Writing alone can't possibly bring a fully-fleshed character into the world, but Skyrim seems like a case study in how lavish production budget and in some cases extremely complicated technology isn't sufficient to make a character memorable, let alone human.