Wikicrawl: "Villain Of The Week"

Another reason for using this format is that it is convenient for writers to supply a continuous and varied amount of challenges for the protagonists to overcome. One perceived "flaw" to continuity-based series is that, if the show is based upon a single dominating plot device (ie: defeating a single reappearing adversary), then should that plot device ever be resolved, the series would supposedly "end". Conversely, if the plot device is not resolved eventually, the premise of the show may become stale. Therefore, a lack of major continuity is often thought to be a convenient solution.

However, in recent decades, many American series have shifted away from this style. A prominent example is the DC Animated Universe, which is covered from Batman: The Animated Series to Justice League Unlimited. While the former series was mostly episodic, with only moderate continuity between episodes, Unlimited is very continuity-heavy--even making continual references to past series. Other American series (both live-action and animated) have also adopted more plot-based continuity. 24, Lost, Gargoyles, and The Sopranos are shows that placed varying levels of importance of continuity while Buffy the Vampire Slayer and Angel mixed both the villain of the week stories with complex, season-long storylines.

-- Villain Of The Week [Wikipedia]