Sucker Punch says that the open world is designed around player choice, letting you focus on specific gameplay elements - like exploration or combat - based on what you're interested in.
Let me start with something I like. Borderlands 4 is a vast, beautiful sci-fi game... Exploration, the hunt for quirky optional fights or hidden (hopefully red) chests has been greatly enhanced.
The sheer variance in the story depending on choices creates a unique gameplay experience, where different NPC reactions and boss fights enhance the narrative.