No show can run a long time as Arthur does without running its course. I haven't seen it in years but many of the issues (repeating episodes, characters becoming Flanderized) could be found in many a long running series. I do want to say that I admire any show like Arthur or Sesame Street that can handle a sensitive subject like cancer and treat kids with enough respect that they can understand it.
A point I make quite a bit, actually. On the one hand, yes... the episodes are a little tired and labored. That is a natural affliction of long running programs. And some programs get tired
really early in their run as well. And considering the show's actual demographic, they really don't care about the episodes being awful.
However, it seems they're sticking to lame kid's show tropes, which is strange and I'll tell you why. A couple years ago, I went to an even hosting Marc Brown. He told this story about how long it took Arthur to become a series, and why it wasn't one sooner. Essentially he was approached by some of the biggest writers in the cartoon making industry and he turned each and every single one of them down because the scripts were inorganic, and in his words, the writers didn't know what it was like to be a kid. Now, hypothetically, this happened in the 80's. Watch a cartoon made in the 80's about a gang of kids. he's right.
The sad thing is, we're getting some really bad 1980's kid's cartoon tropes in the show lately. The Complainer is always wrong (Binky's Music Madness), the crazy treasure hunt adventure (while not a treasure hunt exactly, Around the World in 11 Minutes), and now we got a "too short to ride the roller coaster" episode. They're
so going to find a genie in season 19.