I've been working with a graphic designer for the last few weeks and I've now got some mockups for the card and map tile designs. They look great! I'm not ready to post them here yet though.
I'm reworking the map design to make the buildings line up more, which will means the city has more twists and turns to make it more interesting. The cop has a harder time moving through it. The cop moves more often now, whenever an alarm is set off. Players are going to set off alarms all the time if they're not careful, so there is a strong incentive to do things as sneakily and quietly as possible.
Furthermore, players no longer have the ability to create new cards all willy-nilly. There is a resource management element to the game now, meaning players will have to make decisions about when to create new cards and what kind to create. Someone who makes wise decisions will definitely have an advantage.
The long and short of it is that Thief is now more game-like. It's not just a hilarious romp through a bizarre series of obstacles. This is good!