CREEPY

The internet is filled with lists on popular culture, including vague rankings on televisions shows.

LOST appeared in the Top 10 "creepiest endings" to a television series. Creepy, an unpleasant fear or unease about a situation, may not accurately describe LOST's conclusion, but the list remarks stated:

As if this show was not strange enough, the show's finale added an extra creep factor to it. Though the finale did piece things together, fans who had fallen in love with the various characters were heartbroken, or better yet, disappointed to learn they were all living in purgatory. It made some viewers question whether the characters were ever alive at all.

 It depends on whether you take TPTB's word that the characters were "alive" the whole time (when the purgatory theory was advanced by fans early on in Season 1). But the purgatory Ending did bluntly raise the possibility that the characters were dead all along.

And that doubt is valid because the writers could have done a different, non-purgatory ending, IF they so chose to do so. However, it would not have been "as happy" ending because so many main characters (Juliet,  Jin, Sun, Jack, Locke, Boone, Shannon, Christian) were already dead so you could not have a happy reunion at the island grave yard. For a few, having the characters all dead prior to Flight 815, with the unhappy departed having their souls treated to "one final adventure" in the spirit anteworld called the island, would have been a clearer justification for the sideways church reunion.

It would have been creepier if the final reveal was that all the characters NEVER lived at all; that the entire series was a "what if" these human spirits actually had lived . . . in other words, the final scene would have not shown a church but an operating room door at an abortion clinic.  All the characters were never born. But since they were innocent, the universe gave them the chance to live like humans in a cosmic playground.