This game is surprisingly, ridiculously good! I got it as a gift for my birthday and it's clever, well-thought-out and an absolute joy to play. I normally avoid board games based on stuff, worried that they're cheap cash-ins. This has been damn good fun!
The basic mechanics are that each player attempts to control the city by playing one or more card (of 100-200?) a turn, most cards allowing you to chuck down a minion to contest an area or purchase a building in an area you control. You start with 5 cards and restock to 5 at the end of your turn. It's remarkably subtle and difficult to control an area, requiring cash, no trouble and minions, so planning ahead while trying not to tip off your mates gets pretty conflicted. Each area adds in different bonus rules, maybe tipping off your eventual plan. Add in that everyone has a random personality with secret winning conditions (control the city, keep the peace, ruin the peace, make loads of money, own the city) and you end up trying to mind-game your poor friends.
It fits damn well in the Pratchett universe, as every card is different (seriously; I spent a good 10-20 minutes just looking at the damn things!)
The one bad thing about the game is the playing pieces. Though the board is spectacular and the cards are damn pretty, the pieces are just painted wood chips. It keeps things nice and easy to see, though, as trying to keep track of who's controlling the city can get difficult!
Basically, it's a reasonably mechanically simple game at the core, but if your friends are remotely sneaky, it becomes absurdly devious. Outsmarting each other is absurdly good fun and the wonderfulness of the cards makes it damned awesome to play. Get this game!