I hate to pile on, I really do, but the impression I got from this episode is that LOST used to be Star Wars and now it's the prequels.
"I wonder where Jacob came from?"
But actually SEEING where Jacob came from is not a good idea. At all. And fans of Star Wars should know better than to make that mistake. MIB even had Anakin's "my village is burned" turn towards the darkside. And seeing them as little kids just robs them of any menace or mystery.
It was just completely dramatically unsatisfying. As if the creators used to be excited about telling these stories and now they're just checking things off a list and explaining them in the most workmanlike way possible.
Everytime LOST opens the scope of the show it comes the inevitable but what happened BEFORE THAT!
Ooh, a French transmission. How did they get here?
Ooh, the Others! How did they get here?
Ooh, the Dharma Initiative! How did they get here?
Ooh, Richard Alpert! How did He get here!
Ooh, that crazy statue! How did that get here!
Ooh, Jacob and MIB! How did they get here!
But it keeps forcing them to have to go back and explain these things. Which is never as fun as wondering how they got here. It only leads to now going "okay, well how did their MOTHER get here" and how about the people ON the island already! What it also does is dwarf the significance of Jack and co. from being major players destined for greatness, to being the next in a line of schmucks here for stupid reasons.
Also, DRAMATICALLY it was so unsatisfying to see things this way. Even if they had to present this information it could have been done with a several minute monologue and maybe a single flashback for maximum impact, but to spend an entire episode there just takes all the mystery out of it.
My version: Jacob and MIB are brothers, Jacob is always the favored one by the mother to be the protector because MIB always has a little more anger/unpredictability/temper on him. He is always the 2nd favorite child, the mother dies when they are young (REAL YOUNG) and as they get older the temptation to return to the light becomes too great for MIB and he goes towards it not knowing it will kill him and use his body for Smokey's Evil. This is much more tragic dramatically than Jacob throwing the dude in there. Anyway, oh well this show. Amiright?