A great sitcom is like a perfect band that makes beautiful music. The problem however is that when certain instruments stand out, the band... or... in this case, the show winds up getting rid of other proverbial instruments that make those louder ones sound so good in the first place...
And with Good Times, by the time the series ended, two characters who provided both the lead and the main rhythm section were long gone...
Everyone knows that John Amos left as the father, because this is his last episode... but Esther Rolle took off as well, making it basically the JJ show the same way Happy Days became The Fonzie show...
You need to have a really strong foundation for a strong building to truly last, all the way to the end when it's meant to end, and Good Times eventually was built on sand, crashing into the sea years before it should have...
This is the final episode with the strongest foundation almost gone, and it's too bad. But nothing great lasts forever.