While many (most?) mysteries remain unsolved, Lost's series finale "The End" was, nonetheless, satisfying because it didn't purport to have all the answers. Instead, viewers were comforted with just one: If you live together, you won't die alone.
We finally got to see Jacob, the mysterious man in charge of the Island! In the opening scene, we see him living on the Island, in the distant past, cooking up a red herring.