I'm a big fan of games that use existing, but non-game tech in interesting gamey ways. World Of The Living Dead is a Google Maps based zombie survival MMO. You're a watchful protector trying to guide survivors around real world city streets. You use Maps' pathfinding to set destinations, and the zombie density reflects US census data. You need to manage the survivor's fear, fatigue, hunger and route as the zombies increase their grip on the world.
The complexities are in the micro-management and pondering your moves ahead. Every little detail of the squad of people you're looking after needs managed to drive them through the streets. Overlaid on the the map are missions, safehouses, a well as the raw data of the outbreak scale: the immediate city blocks around you are coloured according to risk, so for everything you do you have to factor in the danger of the surroundings.
When you eventually make it to a place, you can leave messages for those that come after you, encouragement, help, even warnings if you're feeling territorial. There's also a twitter-ish messaging system that does the same, and you can chat to other players, or use it to tell your story. One update reads: "Locations beginning to thin. Density of Zombies growing steadily to the north. Thinking about moving south soon."
I've only played an hour or so, but there's an sense of dread whenever I look away from my browser: the world ticks along if I'm there or not. I'm already pondering telling the survivors to hide so I can get back to work: there's a lot of information to parse, and plenty of missions to leap into, and it feels like it might be just a little too involved as a game to play while at work, even if you need to rest the survivors after running them from place to place. It's rather intense.
It also got me thinking about a game based on hyper-local knowledge: imagine being able to play a game based on knowing which alleyways are safe? In that regard, the place I grew up would be a Deus Ex Revolution style boss fight.