Basically more tools to make custom NPCs be different and have more roles. The first game they where pretty lack depth. And where pretty lackluster.
TLDR: have more options to make custom NPCs feel like part of the world.
When your making a custom character you get another list of options which would have behaviors, items they may spawn with and percentage (or keep it simple with options like always, common, uncommon, rare, almost never, random.)
Have options to choose who they are allied with are they friendly with certain groups or hate eveyone? if they are allied to the player, hate the player, or just don't care.
You can set their skill level since the normal custom NPCs always fought pretty badly. So you can have the option to make near perfect fighters or near useless cowards who run away from everyone.
Option to make shopkeepers and set their list of times they can sell. option for them to able to mug people or steal items. Can they hack? Would they hack you if your hackable? Are they hackable?! Do they only go out at night? Do they drink blood. What if they persistently have a status effect on them, you could make a rare giant monster that roams the lands.
Chose what they say, and actually say it instead of just making one box of dialogue.
Also have them have multiple appearances instead of just the one. Or even give control over that. Choose how many different looks do they have. And more.
I always liked messing with the custom character maker and putting them in custom chunks. And I hope more will be added to mess around with.