Admit it: The difference between good shows and lousy shows is hard to miss. You’ve got My So-Called Life, and then you’ve got Saved by the Bell: The New Class. You’ve got Buffy the Vampire Slayer, and then you’ve got Emily’s Reasons Why Not. While even the worst shows to get aired are probably better (if marginally) than the stuff most of us could film in our basements—in production values if nothing else—few of us need struggle to separate the wheat from the chaff. But what about when it’s all wheat?

It’s when we start analyzing the difference between the various really good shows that the line gets blurry. House vs. Chicago Hope. Veronica Mars vs. Freaks and Geeks. And we insist on doing that, with Emmy awards and Golden Globes and viewer polls, as if a drama’s quality could be measured as simply as we measure height or speed or weight. So fine. Let’s try it.

Here, for what it’s worth, is one measuring stick to consider. Good shows should do almost everything (casting, acting, music, writing) very, very well.

Great shows do that, and more.

I didn’t initially watch Grey’s Anatomy, when it started in the spring of 2005. My bad. I came into it during the second season, just in time for the two-parter “It’s the End of the World” and  …