Simpsons is going through what many shows WISH they could go through... being around so long that even new stuff doesn't seem new or different. M*A*S*H* lasted a long time... as did Star Trek (the original series), Seinfeld... and all of them worked harder in their later episodes to "remain elite" as best they could. Still, people burn out eventually in this "what have you done lately" world. Being a huge cartoon fan myself, I like the Simpsons... but even for me it's getting a little "old". But they shattered the old "record" the Flintstones set back in the day... and that's worthy of a serious "DOH-nut".
