I don't mind a show running a long time, but it should be dynamic. Look at the main characters in NCIS--not a single one has had a long-term meaningful relationship. Gibbs having been married 4 times before the show started then has a dry spell now running on 12 years? I mean sure he had a few short-term girlfriends, but that's a huge departure from his pre-show behavior. None of the characters have moved, gotten promotions (McGee got a title change--whee) and the only regulars to leave the show left because the actresses got tired of it. It's like they're pretending that time doesn't lapse on the show, which is just a huge mark of cowardice on the part of the show runners. They're so afraid of losing ratings that they'll do the same thing over and over again for 12 years. It's crazy.
People still watch it at 15-20 million viewers per new episode, though, and that's all that really matters as far as CBS is concerned.