Oh god, Risen is such an amazing game. I thought my friend and I were the only people that had heard of this game.
My only complaint is that it isn't as open ended as it seems. The item progression is linear and any cool or hidden area you discover, is actually part of the main storyline. Basically, there are no secret areas to find and few extra quests, you have to visit every area and returning to old ones gives nothing new.
But otherwise, it's a brilliant game. I love the barter system where you can trade items for other items directly, instead of having to sell your stuff for gold, then buy what you want with gold. More games should do that. Also, I love the way the story branches out. There are several factions, with no clear cut good or evil. If you talk to one group, they will portray themselves as valiant knights and the others guys as the scum of the earth, but if you talk to the other guys, the roles are reversed. It really gives weight to each decision you make. You have to think things out, because your choices have a big impact on how the story plays out. And of course the graphics are amazing! The game has better graphics than Oblivion and runs much smoother.
So Risen, great game. It's a big inspiration for me, game design wise.