I used to think thought Chester was a pretty much worthless character, but after Festus (and the other secondaries), I came to realize the whining and often inept Chester character was easily the best of the bunch.
The Festus character was a bit too concentrated, making a little bit of Festus go a long way. Festus was an asset is many episodes, but all too often Festus overplayed Festus to the point that it hurt the show. And the comedic Gunsmoke episodes where Festus' half-wit family members visited Dodge City weren't at all funny, they were silly. I couldn't watch much of them.
This comes from a life-long Gunsmoke fan who listened to Matt Dillon on the radio on Sunday evenings before it was on TV. Once televised in the mid-'50s, I seldom missed an episode. The original violent thirty-minute format was easily the best, long before the arrival of Festus.
Gunsmoke has survived the years well in comparison with many shows from the '50s, 60's, and '70s that just aren't worth watching today.