wavering between spiritual and sci fi. In the 4th and 5th season they firmly went sci fi. Then for the 6th season they went firmly the other way and it didn't reconcile.
So we're so supposed to accept all the scientific mumbo jumbo about time travel, the experiments, magnetism, polar bears, sharks genetically engineered AND that all of this operated on an island with some people with super powers to grant no aging and that the people 'created' a purgatory where THE most important people are only those from the island who can figure it all out and move on in the after life?
Even for Stephen King that would be pretty convoluted.
On the production end, I think that most people online guessed early on that they died and the island was a form of purgatory, so the writers went the opposite direction. Then as people figured out the sci fi angles, for the final season they decided to have their cake and eat it too and went spiritual. Also it was the ONLY way they could get all the cameos from characters who died.