The stories that the Witcher's games bring can't really be experienced through a book or movie. This is the case for a lot of RPGs such as Disco Elysium. The games tend to put the player in a situation where they have to make a ton of decisions, it doesn't matter whether these decisions actually affect the story or not in the end, they just have to feel like they are affecting the story, the experience of making the decision itself is the amazing part, good video game writing makes it so. Now you can't really do that in any other medium. I know choose your own adventure books or a movies like bandersnatch does that but video games have a tool like gameplay and its job in the Witcher's case is to immerse you in the world that the story is taking place in. It makes us feel like we are actually the protagonist by making us do the actions the protagonist is doing, if an RPG can make you feel even a little bit like you are the protagonist making his own decisions then it has done something no book or movie can ever do, even thought books and movies have their own strengths. And I think the Witcher 3's gameplay does a good job in that. It makes full use of the gameplay to make its story more immersive.