a) The violencean, or b) the experience and freedom and sense of accomplishment? According to research, the answer is b). There is a video on it:
Video game violence is a concern, and rightfully so because people after all do imitate behaviors based on certain models, and it has been shown that the brain part that has to do with aggression do lit up. Also, blames after certain violent crimes are placed on games, and the question is whether they can be blamed on games. From what I know, certain crimes did increase when TV became very popular. While they are correlations, an onset of one did follow the onset of another one. So it is a complex thing. Of course, I doubt most people go into a criminal frenzy after playing video games, but it is a good area of research to follow.
To end in a lighter note, someone did a Mario Paint music version of a theme in Mario Galaxy. It is an incredibly accurate version: