To add to Uberbanana's fine writeup, Plague Inc. is a fairly addictive strategy game in which you play the role of an emerging, evolving pandemic disease. With most of the disease types, the ultimate goal is to wipe out humanity, but with the Neurax Worm or the Shadow Plague (a recently introduced vampire plague type) you can trigger a victory by mentally enslaving humanity instead. If thoughtful games provide a kind of dialog, Plague Inc. provides the other half of the conversation that Pandemic began.
The grimness of the game's subject matter is alleviated by whimsical alert dialogs, disease scenarios, and achievements. For instance, there's the Santa's Little Helper scenario, which the game describes thusly: "The world is dark and gloomy. Boring governments worldwide have banned holidays, laughter, and celebrations. Humanity has forgotten how to have fun - people dress in gray and spend all their time working. Luckily, the Neurax Worm has teamed up with Santa and is determined to infect the whole world with joy and happiness. Can Santa's little helper make a miracle happen?"
Plague, Inc. also provides enough of a legitimate educational component that it has been used as a gamification element in college-level public health courses.
What can students learn from this game? Geography is one thing. The game screen presents you with a map of the world, and you have to move your plague from country to country, each of which has a different climate and environment and therefore affects your plague in certain ways. A player is bound to memorize those basic details after enough play-throughs.
And students are exposed to the basics of epidemiology and learn about potential disease vectors such as airborne or waterborne spores or sneezes or rats. When local swimming pools started experiencing a cryptosporidium outbreak, in my mind I saw a map of Ohio with little red infection dots breaking out on it: clearly, this disease was exploiting a Water II infection vector and would be harder to wipe out (which in fact it was). So, playing this game is bound to make students think about how local diseases spread, and if absolutely nothing else it is likely to make students wash their hands a bit more often!
The downside to Plague, Inc. from a gamification standpoint is that some educators and students alike may be understandably reluctant to play a game whose goal is the extinction of humankind, no matter how engaging it is. And if that is the case, Pandemic would be a great alternative.