"Content" and "value" are closely related, but they aren't the same thing. Content is what determines value when we are talking about entertainment. An interesting 10-page novel for $20 is a bad value. A boring 1000-page novel for $20 is also a bad value. An interesting 1000-page novel for $20 is a great value. But the value is not the content. The content is what you actually experience when you read the book. The content is the reason why you buy.
For a book, the content is closely related to the story. But games are much more than just a story. The best word for games is just content.
Content is different from gameplay. Mario Kart, 2D Mario, 3D Mario, Mario RPG, and Mario + Rabbids all have very different gameplay. The content of these games is very similar. In any of these games I can experience Mario, Bowser, Goombas, Peach's Castle and all of the other parts of the Mushroom Kingdom. The way I experience it is the gameplay. But the actual world and the stuff in it are the content.
Graphics are experienced with the eyes. Music is experienced with the ears. Gameplay is experienced with the hands. Content is experienced with the mind.
But is it really? For example is in a racing game the world content or the cars/karts or actually both?
Waluigi has different stats in a kart vs toad on a bike making it gameplay but also content
The content is the world and the characters and the karts. So Mario Kart does have a little bit of unique content from the other Mario games (the karts), but it's mostly the same.
Content is not the stats. The stats are really part of the gameplay. Game mechanics and controls are all gameplay. At a certain point during any game, you've learned the controls and mechanics well enough that you don't even have to think about them anymore. All of that is second nature and you experience what the game is really about. That is the content.
Dynasty Warriors and Hyrule Warriors have almost identical gameplay. Maybe the characters that you can choose in one game have similar stats to the other? I don't know. I focus on the content. One game takes place in Hyrule and the other in a fictional version of ancient China. The content of the two games is pretty different even though the gameplay is extemely similar.