It's had at least three different published forms: Web of Power, China and Han. On top of that, Michael Schacht has offered additional maps on his website. Personally, I found the subway map to be strangely hard to process :D
Elevator pitch: the different maps show various regions that have spaces connected by paths. Players play cards to place either forts on the spaces or diplomats on region markers, then draw cards Ticket to Ride style. (Although it predates Ticket to Ride) You get points by fort majorities, forts in a row and the diplomats score by majorities BETWEEN regions.
Trust me, that elevator pitch glosses over tons of stuff. Basically, you play cards to place pieces and try take over areas.
What makes the system really tick is scarcity. You have a limited number of pieces. There are a very limited number of spaces on the board for those pieces. And since most of the cards are for two regions (every map I've seen has one big regions with its own cards), cards are scarce as well. The economy of the game is very tight. Every card you play can be played in many different ways but you only get to do one of them and it's never enough.
While there is a strong tactical element to the game, since you cant control what cards come up and other players are going to do their best to mess up your plans, there's a strong strategic element to Web of Power/China. You need to go in with a plan or you'll get crushed, just make it a flexible one.
I first discovered Web of Power on BSW back in 2003 or 2004, including some speed games that played out in less than five minutes. I picked up China as soon as it came out. And I get in online games on Schacht's own site. I've had years of fun with this family of games and that doesn't sound like it will end anytime soon.