I wonder if it's possible to get that painterly feeling into a 3d-environment.
Why do you want that? A 3d environment, that is.
Other people have already answered this very well.
What I dislike with most 3d, the way it looks today, is that the presentation of the world is very objective. 3d rendering is almost always about pure math - you're computing how a certain 3d model would look from a certain angle. A painting is usually a
subjective presentation of a scene.
If you make a painting, who cares about whether you got lights and shadows mathematically correct? It's about the mood and atmosphere, not the accuracy. Celshading is an example of how you can ignore the mathematical accuracy and go for beautiful results - there should be more ways to do it, to emulate paintings or completely new graphical styles.