This episode is our introduction to Festus Haggen, who will eventually replace Chester Goode as Matt's sidekick and "comic relief".
As episodes go, it's an uninspired story of Matt having to bring in a man wanted for murder, with its various clichéd reversals of "who's on top".
But these don't matter, because its purpose is to introduce us to Festus. And that it does exceptionally well. Matt runs into Festus at a farm where Festus' murderous uncle Blackjack has killed a man. Festus says he's after Blackjack, too, for having left his twin brother Fergus to die. Matt isn't sure he can trust Festus, and their discomfort with each other is convincingly dramatized.
Festus is not yet the character we know and love (or are annoyed by). Ken Curtis has not yet "squinched up" his face, or folded his right ear under the brim of his hat. Nor has he settled on the "squealier" voice we immediately recognize (his vocal delivery is more like that of Andy Griffith), or pushed Festus's bow-legged walk to its limit. He's also slier and wilier than the later Festus.
Oddly, no one can decide how his name is pronounced. Both Arness and Curtis pronounce it /both ways/, with a long A and a short A. You'd think the director would have caught this and enforced a single pronunciation. (According to the rules of English pronunciation, Haggen is pronounced with a short A. I prefer the /sound/ of the long A, as it's firmer and more "masculine".)
Ken Curtis gives a typically nuanced performance. He was a fine character actor, and throughout the series showed his versatility, convincingly playing a mixed-ethnicity Indian scout; a ladies' man; a plains hunter. Among the cast, only Dennis Weaver was a "better" actor. The final version of Festus was not his most-subtle performance, but it showed how an actor can be "over the top" without looking campy or stupid.
For those who feel Festus should have remained the way he originally was... It would have upset the show's balance. "Gunsmoke" generally tells dark stories, and though Matt has a sense of humor, it's not a major part of his personality. Matt is a laconic, no-nonsense person, and a sometimes-silly sidekick is needed to balance it. A always-"serious" Festus would be too much like Matt, breaking a basic screen writing rule ("Thou must not have two characters with the same point of view.").
And there's another reason. In this episode, Festus has several well-written scenes -- and Curtis walks all over Arness in them. He's the better actor, and at "serious" moments, it's all too-obvious.