I'm gunna go out on a limb and say that, although I have never watched SS regularly since I was a youngling, I slowly grew to dislike the fact that Big Bird just appeared everywhere and was the main character of almost all the home-videos, etc. I felt that it was he, before Elmo, who hogged the spotlight away from such characters as The Count and Ernie and Bert.
Of course, later on in life, I figured that he was kinda "meant" to be the Kermit to SS's Muppets...but I think the key to SS is variety and keeping a core group main. Never ONE star be that star Big Bird, or Elmo.
Just my 2.2 cents.