Games which are directly educational are notoriously crappy. I'd have to say that a large part of this is probably due to a lack of inspiration and passion by the developers. Furthermore, kids are naturally averse to blatant attempts at education, because the stereotype is that school is lame.
But you see, games don't need to teach math, science, grammar, or history. The things that games can teach are far more important, they can teach people how to think. Even in my limited teaching career, I've come across several people who don't seem to know how to recognize patterns. I'm not talking about seeing a list of numbers and knowing which one come next. Many of my students don't seem to realize that they already have the tools to solve a problem, they don't realize that they've done a problem before, or that a new problem is a simple combination of two or more old problems.
Games teach you how to learn and think in a natural way. Failure is discouraged and success is rewarded, new problems are often combinations of old problems and can often be easily recognized as such, and trying new things is encouraged. They also help teach you how to react to stressful situations, and how to react to change. Video games may not offer much in the way of knowledge, or skills, but they mold your brain into something that is more functional. We need to end this bias that video games are bad for you. Video games are good for you, but like all things, must be taken in moderation.