The rules variant are not much and they are done to serve the setting, the character generation is the same, just that races are all in the setting book, more powerful than standard, and most classes are not there because of the way the things are there.
Every change is for flavor improvement and it works pretty well!!
If you want to get inside the world of midnight you have to go to
www.againsttheshadow.org
The Midnight fansite, and also you can know more about it at FFG,
http://www.fantasyflightgames.com/midnight.html
Hope this helps, there is a map and a preview, aside from the short story, true teasers.
