Across the Sea, in opinion, was a very good episode but not my favorite. A bit like The Other 48 Days, but with 2 badass immortals. I liked it, I enjoyed the backstory of Jacob and MIB, but the episode from beginning to end was only a 'pretty good' story, considering the hype it got as the 3rd last episode that will reveal all about the island. The reason I absolutely loved it in the scheme of the entire season, however, is because it's completely changed my viewpoint of all of the Jacob/MIB dynamics. I have a feeling that going back and watching from the Incident on, I'll have a very different perspective, knowing how Jacob and MIB came to be enemies. From 'it always ends the same', to 'I want to go home', to 'The devil took my body' (Those were the Incident, LAX, and Ab Aeterno btw), I'm going to enjoy rewatching season 6 much more now that I understand the characters, their history, and their motives so much better.