Mount and Blade Warband for me. Native is fun but the community has made so many total conversion mods for it that can be swapped in and out at the launcher. It can be Game of Thrones, Lord of the Rings, most points of history between now and ancient Rome, and it can even be Star Wars
Awoiaf (GoT)
Last Days of the Third Age (LotR)
Warsword Conquest (Warhammer)
Perisno + Prophecy of Pendor (Fantasy conversions with lots of lore and things to do)
Gekokujo Daimyo Edition (Sengoku period Japan)
Anno Domini 1257 (13th Century Europe)
L’Aigle (Napoleonic Wars)
https://www.moddb.com/games/mount-blade-warband/mods?sort=visitstotal-desc
Theres tons of them on Moddb and they’re easy to throw on your game