Best summary so far was made by Bart Simpson, "it was all the dog's dream".
Best movie analogy to the ending is Jacob's Ladder. The movie keeps switching between ever more bizarre scenes, ending where the main character's dead daughter leads him into the light, then the movie returns to reality, where it's revealed that all the scenes in the movie were just the hallucinations of a soldier dying from a combat wound.
I never like ghost story movies like "sixth sense" or "the others", since they are usually full of plot holes and/or keep changing the rules and/or require some incredibly unlikely series of random events.
So I'll bump it up one step from Bart's summary and state that it was all just Jake's hallucinations as he died from the plane crash, then again he could have been dying from something else and the plane crash was part of the hallucination.
I never watched Lost, but seeing that there were only seven or so episodes left, I was hoping that it would end up with good story line. There was another mediocre sci-fi series called DollHouse, essentially a story line that wasn't really going anywhere because there was no end date. Once it was announced that the series was ending, the writers responded by creating a coherent story line that ended up being reasonably well done.