Pretty cool, but it tends to lag at times. Also, you should be able to remove/sell/destroy buildings again. I accidentally boxed in the backside of a gold mine with farms. It didn't look like the peasants wouldn't be able to pass anymore, but apparently that was the case. And, apparently, peasants only exit the mine on the back side, so I was unable to haul gold and had a bunch of trapped peasants in a corner. Also, unselecting peasants etc. is a nuisance.