A dark strategy game called Plague Inc. recently infected the top spot in the iTunes App Store. It puts you in charge of the evolution and spread of a globe-spanning virus, and as the epidemic spreads, your disease has to develop new traits, symptoms, and levels of deadliness to avoid immunization and eventual obliteration. Plague Inc. follows in the wake of Pandemic, a popular web-based Flash game from a few years ago which has recently made the jump to iOS.

The goal, of course, is to wipe out humanity with your very own disease. Every area of the planet has particular qualities that will affect the spread and strength of a virus; for example, it's hard to infect developed nations with tight border control and advanced medicine. As you play, the world reacts according to your progress, so the more severe your strain is, the more aggressively governments will fund research and shut down airports. You learn about these reactions through a fictional news ticker with some cute tongue-in-cheek headlines such as "France considers banning employment" and "Large Social network IPO doesn't meet expectations". After beating the game a few times, you unlock new kinds of diseases with various attributes, like fungus, which can travel long distances without much effort, all the way up to bio-weapons.

Over the course of gameplay, DNA points pop up across the map which you tap to gather and use for evolution. Before a region is ripe for DNA gathering, you'll have to make sure to tap the biohazard symbol first to lock in the initial infection. Similar bubbles will pop up over countries that are developing research against your virus - be sure to pop them quickly to slow down their progress. Once in awhile, new symptoms will develop on their own without you having to spend any DNA points. Equally, sometimes humans will randomly make a scientific breakthrough against particular symptoms, forcing you to be on your toes and readapting.

As you progress in new evolutions through various infectivity, severity, and lethality trees, they'll often meet at high-tier abilities; for example, maxing out water and air infectivity will eventually unlock "Extreme Bioaerosol", which can bypass all sorts of man-made filters. The symptoms tree has a whole bunch of similar deadly combinations. That customization is really what makes the game interesting; even if you're infecting the same world over and over again, there's a ton of depth in exploring which mutations are the most effective, and how to best adapt to panic and human research.

Most of your time, you'll be looking at a world map broken up by region and watching boats and planes traverse the world. Despite the fact that there aren't particularly high expectations in the graphics department, the dotted red lines trailing infected travel are pretty blurry, even when zoomed all the way out, and the world map is especially pixelly when you're playing on the iPad. Even the style of the airport and port icons are barely different from Pandemic 2.5, which clearly signals where the developer got their "inspiration". Pandemic 2.5 has Plague Inc. beat in terms of style and graphics, though not necessarily gameplay. There isn't much to say about the audio in Plague Inc., since you're mainly just tapping the occasional pop-up. Though there's some pretty flavorful text portions of the game, some of the writing is downright lazy, including miscapitalization and missing punctuation.

OpenFeint and Game Center are both employed to handle achievements and high scores. I would be curious to see what a multiplayer version of this game would be like; I suspect it would be similar to Defcon, in that either players were trying their best to wipe out as much of the planet as possible, but there could definitely be some interesting hybrid viruses that could evolve from the two working in close proximity to one another. There is cloud saving support, which allows you to pick up your mass genocide where you left off on either iOS device, but keep in mind that games have to be saved manually before you quit.

The good

Extensive customization
Fun (if sadistic) gameplay
Good bits of humor amid all the horror

The bad

Choppy world map graphics
Poor writing at times
Slightly unoriginal

The bottom line

Although the subject matter might be a little on the grim side for some, Plague Inc. has a deep level of customization that will have you coming back regularly to try new strategies. It would be nice to see an added layer of polish to the game, such as tidying up the writing and offering smoother graphics similar to what we've seen on the spiritual predecessor, Pandemic 2.5. Still, the core gameplay of spreading slowly across the globe and gently guiding it through challenges with the right changes is a really interesting experience. Normally, a player claims very specific control over something, but in Plague Inc., you're just as much of an observer. If you're into leaning back and watching chaos blossom like a terrible, terrible flower, Plague Inc. is worth the $0.99.