I've been thinking about educational games as well. The main problem, it seems to me, is that trying to make learning fun for someone who isn't already interested and motivated is a waste of time because you're just trying to hide the teaching under a sugarcoating of computer game, and that never works. On the other hand trying to make learning fun for someone who is already interested and motivated is pointless, because they already want to learn and the game just adds needless hassle like completing levels in order to reach the next piece of knowledge, or whatever game mechanic you're using. It's a pity, because I think of the way games like Portal build up complex puzzles from simpler ones and use the level itself to ask the player leading questions, like a kind of visual/spatial socratic method, and I think there must be a way to use that to teach, espiecally mathematics where visual/spatial metaphors could easily translate into mathematical metaphors... but I just can't come up with a concrete version of the idea that wouldn't be boring or stupid.

Lately I've been thinking that the fastest way to get to grips with a new subject is probably just to memorise big chunks of information without trying to understand it, using techniques like a memory palace and spaced learning programs like Mnemosyne and Anki, then think about what you've learned later, and insight might strike you. This would be espiecally effective if you combined it with a social precommitment to teach your knowledge to someone else, or to take part in a competitive quiz.