I think the term is "Jumped The Shark". Referring to when Fonzi on "Happy Days" was water skiing and had to jump a shark to complete a competition. In other words, the pivotal moment in a show when it all goes downhill. Go to
www.jumptheshark.com for those great moments in your favorite shows. I'll still watch though. I started watching SG1 about a year ago and have some backward catching up to do. SG Atlantis is pretty good too.