Deep Silver has released a 1.1 GB, multi-language demo of Risen, just one day shy of the game's worldwide release. An issue with the demo's executable has caused some sites to pull it down, but you can still grab a (working?) copy on the official Risen blog, AtomicGamer, Gamer's Hell, and WorthPlaying.
If you find one that's working for you, a quick comment below would be appreciated.