Overall, The Witcher games aren't about the gameplay. They are about the story, characters, and world. The first game even basically built its entire combat system around encouraging an understanding of Witcher fighting styles and how they used them to deal with specific monsters. And while the second (and likely third) are more traditional in their gameplay, they still are (or likely will be) very much about experiencing the world over the combat itself.
Also, while the games are less afraid of mature content than most, that isn't all there is to them either. Yeah, the first game had that card-collecting mini-game (the stupidity of which the developers seemed fully aware of), and the second game also had plenty of moments where it took too much pleasure in that content. However, people definitely spend too much time focusing it. There is a lot of stuff going on in The Witcher games, and the rather juvenile approach to mature content is just a very, very small part of what is there.
Also, while the games are less afraid of mature content than most, that isn't all there is to them either. Yeah, the first game had that card-collecting mini-game (the stupidity of which the developers seemed fully aware of), and the second game also had plenty of moments where it took too much pleasure in that content. However, people definitely spend too much time focusing it. There is a lot of stuff going on in The Witcher games, and the rather juvenile approach to mature content is just a very, very small part of what is there.