I'm watching Cheers for the first time since it ended. Here are my thoughts:
1) The Rebecca years are as good as the Diane years.
2) Woody is even stupider than I remember.
3) Fraser is different in Cheers than in his own series. He's less snobby but more erudite in Cheers than in Fraser.
4) The writing is remarkably good, episode after episode. And the show often tackles big issues in really clever ways. The Bar War episodes, featuring the rivalry with Gary's Old Time Tavern, are really about the Cold War and the arms race. The third Bar War episode, for example, is a hilarious version of Fail-Safe.
5) The show holds up in part because there are almost no topical or pop cultural references. Cheers focuses on the battle of the sexes, the clash between rich and poor, and tensions between educated and working-class people. In other words, its comedy is focused on universal conflicts, not on time-specific references.
6) The shows theme is, surprisingly, depressing: Everybody loses, always. Sam loses Diane, Rebecca, and the bar. Fraser loses Diane and Lilith. Norm loses job after job. Cliff is just a loser momma's boy, who couldn't get into the army and became a postman instead. Carla is cheated on by most of her husbands; the only one who's faithful to her dies. Diane is desperate to become a great writer but is always getting her material rejected. Rebecca is desperate to marry rich but ends up marrying a plumber. Robin Colcord loses his fortune, power, and reputation. The only one who wins out is the humble hick, Woody, who marries a rich blonde. But he's so numbingly naive that he doesn't fully appreciate his success.
7) The dialogue is incredibly sharp and often aphoristic.
Overall, I am stunned by how many truly great episodes were produced.