One primary reason for the show's success is the characters. Fans became fanatically attached to the group. None has more of a following than the self-described "Everyman" Hurley, played by Jorge Garcia.
"We're not a cop drama and we're not a hospital and we're not lawyers. Our characters are people you want to know more about and want to, you know, come back to," Garcia said.
It's a diverse collection of souls, among them a spoiled brother and sister, an estranged father and son, a pregnant Australian woman, a brittle Korean couple and a former Iraqi soldier, Sayid.
Naveen Andrews, who plays Sayid, said this diversity adds to the show's appeal. "It's this group of individuals from all different walks of life -- different races, cultures, backgrounds -- and it's a kind of microcosm of society at the moment," he said.
"What's interesting is that you find characters are suddenly set free from the way they were defined in the other world," he added.
That's certainly true for the character of Jin, a Korean who speaks no English. The actor who plays him, Daniel Dae Kim, says it's a character that breaks the movie stereotypes of Asian men.
"Very rarely have we been in a position to be seen in a positive light. Asian men tend to be made fun of and jokes are made at their expense. And we rarely see them as heroes or romantic leads. ... I've worked in this business now for 12 years and this show gave me my first on-screen kiss," he said.
Another character, Charlie, was a fading rock star and heroin addict who stole from his girlfriend's family. He's played by Dominic Monaghan, who made a splash as the hobbit Merry in the "Lord of the Rings" trilogy.
"There's a lot of characters in the show that seem to be having to face their demons, you know? The thing with Charlie is that through his addictive kind of lifestyle, he now has issues with women and with trust and with intimacy and I think, for want of a better word, Charlie is lost," Monaghan said.
Character development is crucial, the show's creators say.
"The complex storytelling -- moving backward and forward in the character's lives -- shows an attitude toward the viewer some say is unusual in network programming. The audience is intelligent. They are very savvy and you can't talk down to them," said.
The creators say another reason for the success of "Lost" is that they draw from powerful influences. They use a story structure associated with movie suspense master Alfred Hitchcock: The audience knows things the characters do not.
For example, we know that the mysterious John Locke, played by Terry O'Quinn, was an office drudge at a box company and in a wheelchair before the crash.
The characters on the island know him only as a survival-savvy hunter. Locke is one of the most popular characters among show fans.
O'Quinn said he thinks the audience likes Locke because "he's enigmatic, because they don't, they can't pin him down. He seems to know a lot, and he knows about people."
Locke also seems, more than any character, to feel like the island is mystical -- that there's something supernatural about it.
In a cast kept in the dark about the island's mysteries O'Quinn is the only one who got a hint about the invisible monster. But even he doesn't know what it is, and he appealed to Lindelof for guidance.