30 Rock
While they are very different shows, I can't help comparing them. Maybe if Studio 60 would have been a little more like 30 Rock, it wouldn't have gotten cancelled. Why? Both shows have a similar concept, the making of a comedy show, dealing with network executives, ratings, advertisers, actors and writers. However, the tone and the mood are what make them different from each other. 30 Rock is a sitcom, it exaggerates conflict, the humor is light and the characters are clear comedy archetypes. While Studio 60 is more of a drama with humor (smart and sophisticated humor, IMO) with complex characters, interesting and strong conflicts, yet somehow it became boring and it tried too hard to moralize television.
Studio 60 took itself way too seriously for a TV show about making television. The West Wing (also created by Sorkin) was a success because politics are inherently taken seriously and intense drama is expected. 30 Rock became a hit because it was fun to watch outrageous characters doing comedy, not serious people with a moral agenda struggling to change television. Maybe if Studio 60 had had a different approach, lighter and a lot less pretentious, audiences would have kept on watching it. It's a shame it got cancelled because it is a TV gem. It's one of the best written shows I've ever seen (even better than 30 Rock). But they missed the tone, they should've gone for something less complex... more like what Tina Fey did with 30 Rock.