If you could divide the series of Lost into three acts, which seasons would you choose for each of the acts? I would choose Seasons 1-3 for Act 1, Seasons 4-5 as Act 2, and Season 6 as Act 3.
Act 1: Crash on the Island Act 2: Be Menaced by Smokey Act 3: Escape from the Island ...whoops, the story didn't end... Act 4: Change what the story is about Act 5: The story is now about the characters being BFFs Act 6: The characters die and become BFFs forever in Heaven, the end.
That's how I would do it. To me, Seasons 4/5 is the Empire Strikes Back parts of the series, which explains why I love them so much.