Games like Dance Dance Revolution, Guitar Hero, Karaoke Revolution and Audiosurf aren't just music games, they're games that take existing music, and recontextualize it into gameplay, giving players a new way to experience music they might already be familiar with, or exposing them to new music with the tantalizing promise of a fun game. Without music, these games are just about timing a certain color or shape with a certain button press. They're playable with the sound off, but they're not nearly as compelling.
In the past year or so, some game developers have started toying with applying this same approach to text.
In my career as an educational game designer, I mainly focus on the problem of getting a set of learning objectives that are met through gameplay. This approach works very well for teaching skills, but I don't think it's as strong an approach for teaching knowledge. There are just some things you can't learn by doing. Like the capitals of all the states, or the multiplication tables, or other things that are really more "memorization" than they are "learning".