Spectre of the Gun. I can't fathom why this episode is disliked. HAD they in fact gone to a "Western Planet" ("Archons" was close), like they went to a Nazi Planet, Gangster Planet, Rome PLanet, then yes, this would simply have been the "Western Planet" one.
But they spun straw into gold and made the super-cool, surreal, great character-acting, interesting premise, great soundtrack episode.