Player agency is the most important part of any video game. However great the combat might be, or however good the graphics are, or even however big the open world is, the player needs to be able to meaningfully engage with the setting, or else they're essentially paying AAA prices for a movie. How games do this varies from genre to genre, of course, and has also evolved over the years. Boomer shooters with destructible environments were among the first to tout this agency in their games, and so were early RPGs with branching stories.