This is one of my favorite episodes because it's interesting to see how one man, Locke's father, can affect two men, Sawyer and Locke, so differently. And yet, in the end, they both need him to die.
This episode also introduces the idea that the survivors may in fact be dead, and that the island then must be some kind of afterlife/purgatory. I'm not too hip to this idea, but perhaps it's all just a lie. Back to Sawyer and Locke. It was really satisfying to see both men finally move on because we all really know they have much more greatness in them ready to be developed. This was a wonderful turning point in the series, and I'm looking forward to seeing how both men change.
Three seasons of character arc come to an end here, and the payoff was spectacular.
A final note, I usually see plot twists way ahead of time, but I never imagined that Sawyer and Locke's history could be so believably tied together.