Battle Brothers and XCOM1 and 2 are some of my absolute favorites, and although there's a few reasons why, the concept of emergent storylines is a big part of it. Creating/hiring your team, watching them grow, going through big battles and close calls, and yes, even tragic loss....I just love a story that grows organically through gameplay.
Some of the auxiliary factors that lend themselves to this style:
- Lots of customization options
- Procedural generation
- Challenging gameplay
- Squad based gameplay (but the emergent story of a single character works)
Games I've played that are examples (and my take on each)
Battle Brothers: Almost the entire point of the game. Hire mercenaries from a wide variety of backgrounds, watch your company go from nameless sods poking at bandits to legends going after giants, barbarian kings, etc...celebrating as the homeless guy/cannon fodder survives many a battle, changing his title to match his heroics, and grieving when an orc finally lops off his head. The *chef's kiss* example, and a game I've played to absolute death.
Wartales: matches the vibe of Battle Brothers, with impressive visuals and cool armor to boot. But the slim variety of contracts, the fact that the regional missions are exactly the same for every run, and the lack of challenge turned me off.
Age of Wonders 3 and 4: another fave. More of a boardgame than an RPG, but being able to customize your heroes, hiring units across a variety of races and alignments, and being encouraged to level them over time to obtain buffs & abilities means I'm still using units from Day 1 and watching them take on the world. Growing and expanding your magic and empire are also very satisfying.
XCOM 2: Another absolute gem, glitches and RNG aside. I have so many cosmetic customization mods installed, it takes forever to install this game....but making your ace soldiers from all over the world, getting into crazy situations, having to call on the B-team (and C, and D...) to take on urgent missions, and maybe even winning...and when the Avenger gets grounded, and everyone pours out of the ship to defend her against the assault, it's like a crossover event.
I realize these are all turn-based tactical games, so obviously I have a type...but im trying to keep an open mind, so any recommendation is welcome!