I played Risen 1, here is my personal (!) opinion:
Risen 1 is super boring! Theroretically there is a lot to do, but you simply don't want to. The story isn't very addicting or witty, the characters you meet are petty and replaceable, your tasks are boring (gathering stuff, walking from A to B...), the enemies are unimaginative (wolves, fire flies, some random guys with swords and shields, oh yeah...) and the worst: The ending is not satisfying. Depending on you playstyle you will need 30-50 hours to get there, but I found those hours to be a waste of time. The only reason why I didn't quit earlier was that I was waiting for something interesting to come, but... nope.
The only good thing I remember is the graphics. Towns, houses, the island in general looked pretty good at their time. But after all, Risen 1 is a perfect example for quantity over quality. That being said, I'd definetly go for Two Worlds 2!