[manasecret]

I liked that episode a lot. It played very well with the themes of the series and how it caused Jacob and MIB to be who they are today, and in turn how that affected all others that came to the island. For me, keeping continuity with themes is more important than all the little details.

Some themes it touched heavily on:

Good vs. Evil
Fate vs. Free-will
White & Black
Games
Life & Death
Pregnancies
Secrets
etc.

The most important play on who Jacob becomes is at the moment when he must make the "choice" to be the island's protector. He physically could have made the choice not to become the protector, he could have walked away. But from all the events that led up to that point and from who he is inside, he really had no choice. Is it fate, or free-will?

On another note, keep in mind that there is still time for other characters to discover a little more of what is the "light" and so on. But if you're mad now, I wouldn't hold my breath for an ending that makes you happy.