It has a lot of really cool technology -- walls where you go through and are washed or clothed, including a "suit wall" where you go from inside to space and the wall puts the suit on you. They make gestuers to "conjure" pieces of furniture or cause things to happen. This is a wonderful place and they all know it.
The habitats are all different -- in shape, size, and intention. One has people who are purposely in coma, one has people who change what they look like for real, many have people who change what they look like in abstraction. Everybody sees abstraction -- a computer network shows how people want to look -- and the prefects carry glasses to see what they really look like. The computer network, the Core, also handles the polling -- everybody is constantly polled about things, some as small as whether one habitat wants to change flowers, some as large as whether the prefects are allowed weapons.
The prefects work at Panoply, a habitat-like place, and they make sure polling isn't cheated and that people who do bad things get justice. There's several levels of prefects and our protagonist is a Field Prefect with two Deputies.
Our primary case is caused by a machine intellect that wants to take over all the habitats, kill all the people, and put in nice machines. It's very complicated in how they work on it, what they find, and who does what.
I really liked this one, in some ways better than the others. I can't recommend which order in which to read it because if you read it first, then you know all the wonderful things that happened before the other books. If you read it last, you already have knowledge of some other things, like hyperpigs. But you should definitely read it.