Imagine a world where you can't die. Sure, you can suffer from disease, be shot, get wounded horribly, but you can't die. You're immortal, just not invulnerable. Now imagine a world where that's the case for everyone in the world. No one can die.
The mad complexity of Lost merits a grand, glorious finale that will keep people talking for years to come. If the show's writers don't deliver, we may never again see a show as demanding and uniquely entertaining as theirs.