18. Lost, Season 3 (ABC; October 4, 2006 - May 23, 2007)
The weak first half of Lost's third season resulted in some soul-searching. The flashback technique of the series was growing stale and the character revelations from the past began to feel repetitive. In response to this problem, Lost's producers limited its focus on the main characters, which further aggravated fans.
Locke (Terry O'Quinn), who had been a fan favorite and was on screen more than almost any other character, appears in only half the episodes of season 3. The new characters, Nikki (Kiele Sanchez) and Paulo (Rodrigo Santoro), were not hitting with audiences. Co-creator Damon Lindelof went as far as to admit that the couple was universally despised. This led to a hiatus to re-focus the show.
Though the second block of episodes came back with a vengeance, making a number of improvements, including getting rid of the offending new characters, the damage was already done.