It was the cold openings. The first season or two arguably had the slackest, dullest, all-around unfunniest cold openings in series history. People tuning in during the first two seasons watched a blah cold opening and must've thought, "Well, if the rest of the show is going to be this bad..." I mean, just start the episode and lets get going I don't need these lame sketches at the beginning that have no bearing on the plot. Not to mention all the time spent writing these sketches could've been spent working on the scripts of the actual episodes.

I don't know I like most of them. But then I was only about 12 years old when the show started. I don't know about anybody else but for me I just didn't think either Sam or Diane were that likable at first.

Ed.

I never minded either the cold openings or Sam and Diane.

The reason why Cheers tanked in the 1st season is because people found it dull. But thanks to Brandon Tartikoff (and the iconic Where Everybody Knows Your Name), it slowing became a successful show. Also with the help of The Cosby Show, Cheers helped boost those ratings.

Also people started asking for music sheets to Where Everybody Knows Your Name.