In the long run I love much more DKS than Risen. But Risen has his own nice thing's. But the skill system in Risen do not match with my playstyle.
To be honest : I've stopped playing Risen since months (now I'm L 10 hero I believe) and have only eyes, ears and feelings for the Dragon Knight Saga, which I really love more and more !!
I've been jumping around between Oblivion, Risen, and DKS lately. It's fun because I can play one for a couple of days and tire of it (The leveling systems are all very different so it's good variety), then switch to another one. I really enjoy the story of DKS and most of the fights, but it's fun to switch between different stories and playstyles. And I'm anticipating Skyrim, of course.