Generally it's a thing in the arts that people start out dark and angry and then mellow with age. Usually, the early period sees the artists producing her/his best work and the quality tails off with the mellowing process. I've been noticing increasing numbers of anomilies to this general rule.
I've mentioned before about prefering the under-appreciated later work of certain goth bands (notably Coil). Another good example would be Blonde Redhead. I don't like anything before their recent "sell out" album, which I think is kinda good. Then, of course, there's Jonathan Richman... Of course, these are my opinions and it's the opinions that are anomolous. Most nerds would disagree with me and the rule would stay in place.
Then you have people who start off producing mellow, charming work and then go all dark. The two who spring to mind are Gilbert Hernandez and Lukas Moodyson. Compare the early "Heartbreak Soup" comics to the joyless, pornograhic crap Beto pumps out now. Or compare "Show me Love" to "Lilya Forever". Jesus! What happened to these people. Are there any examples of this happening in music?