Like the situation with Nikki and Paulo in Season 3 and her own status (along with Daniel and Miles) in Season 4, Charlotte is credited as a principal cast member at the beginning of each episode (meaning she is an series regular, regardless of anything else) but appears on the guest cast lists of press releases via ABC Medianet, likely due to her being dead by the fifth episode of the season. Charlotte did, however, appear in official ABC posters/promo pictures for Season 5.
This is the first season to not have any new cast members joining as regulars.
Season 5 is the first to eschew the traditional format of an on-island story interspersed with flashbacks and flashforwards focusing on particular characters. Generally, the first six episodes employed only one opening flashback for the episode's central character, with the rest of the episode devoted to both the Oceanic Six in 2008 and the remaining survivors jumping through time on the Island. This does not apply for all episodes:
"Because You Left", though arguably Daniel-centric, does not devote greater than usual attention to that character's story and can be considered to lack a central character.
"This Place Is Death" does not include an establishing flashback, but is clearly focused on Sun and Jin, due to the large part that the two characters played in the episode.
As of "The Life and Death of Jeremy Bentham", with most of the principal characters (save Desmond) back on the Island, the series appears to have returned to the old storytelling format. It appears that the episodes will jump between 2 different time periods on the Island as of now. (1977, 2007)
Plot:Kate discovers that someone knows the secret of Aaron's true parental lineage. Meanwhile, the dramatic shifts through time are placing the lives of the remaining island survivors in extreme peril.
Flashback:None; this episode continues storylines of those on and off the Island without delving into the past or future of any specific character. However many fans consider the episode to be Jin-Soo Kwon and Sun-Hwa Kwon centric, due to the focus on these characters.
Plot:Locke takes on the burden to stop the island's increasingly violent shifts through time as Charlotte's condition worsens. Meanwhile, Ben hits a roadblock in his attempt to reunite the Oceanic 6 and bring them back to the island.
Plot: Suspicions about a possible breach intensify after Ben is taken from the infirmary, and a reluctant Miles is forced to work with Hurley when he's asked to deliver an important package to a top Dharma official.
Flashback:None; this episode continues storylines of those in the Island's past and present without delving into the past or future of any specific character. However many fans consider the episode to be Richard Alpert centric, due to his prominence in both the past and present storylines.
Plot: Jack and Kate find themselves at odds over the direction to take to save their fellow island survivors, Locke further solidifies his stance as leader of "The Others," and Sawyer and Juliet come under scrutiny from the Dharma Initiative.