TomC : very good idea to use a game to learn something new (after all, that's why natural selection invented "playing" : to let us learn new skills without lethal downsides...)
There's a vast body of knowledge about gamification, games for learning and everything around it. The sad thing is that nobody trully understand what's going to 'stick'. In fact, you need to be a master of two field to do something good like that : be a true expert of your field (to provide the content to learn and divide it in understandable chunks, with a logical progression) and be a very good game designer. If not, you're going to provide a glorified multiple-choice questionnaire...
The most basic way to learn new things is by unconscious absorption : everybody knows the musical theme of Mario, and can hunt-and-peck the keys on a keyboard to match the tones, even if they have no musical inclination nor seen the printed musical score.
You just "learned" it by being presented the material all the time while playing.
The next step is to fuse the objects to learn inside a gameplay mechanism. For example you can find japanese kanji learning games that ask you to match tiles on which the kanji and their meaning are drawn. It's a memory game (and not a very fun way to learn that information).
A step further is to add a narrative and real game outside the learning part. In that kind of setup, you use what you are learning as a tool inside the game to do some actions, but not all of them. The stuff you are learning are one kind of gameplay mechanism. (An example of that kind of game is 'Knuckle in chinaland', where you play some kind of a JRPG game with Knuckles from Sonic & Knuckles. You move around, talk to people, try to find your way and you battle with ennemies by using kanji cards that you are learning).
Another example : with Adventure Bar Story, you are learning recipes of japanese meals by doing the job of a... japanese meals maker (sort of...)
In SpaceChem, you learn chemistry interactions and bondings as a side product of playing the game.
The more abstract the game, the less graphical content you need to provide, but the more intelligent you need to be in creating a mechanism to learn that is not boring (and if you are bored, you're not going to learn anything).