And just to add to what Miriel said, I have no problem with supernatural or paranormal explanations at this point. In fact, I honestly expect them. But we're not getting that much. This is pretty much what we got last episode as far as answers:

"Why can't Jacob and MIB kill each other? How did Jacob become the protector of the island and become capable of things like making someone immortal?" Because Mom made it that way.

"Why is the island so important and why is Jacob trying to protect it?" Because of a yellow light under it. "Well what's the yellow light?" We'll get to that if you're lucky, but probably in the last five minutes of the finale so you have no idea why protecting the island is important until the very end.

This isn't even a bad explanation because it explains nothing. The fact that their was someone protecting the island before Jacob was kind of a given since he assembled candidates to replace him. It doesn't even hint at answers to any of those questions. I could even accept an out there supernatural explanation; hell, I read comic books so my tolerance for out there explanations is pretty high so long as it's plausible and fits the universe that's been created. But that was like answering those questions with "because." That doesn't fly, and this late in the game there's no reason to still be holding back the way they are. And I think that's what's bothering me the most. We were promised answers and two episodes from the finale they're still playing coy and leaving almost everything for the end.

I will say that the only redeeming quality of that episode was seeing the relationship develop between Jacob and MIB originally. But given the potential for an episode like that to answer major questions, the fact that it didn't really overshadows the good parts for me.