This episode has a nice look at the characters Jin and Sun's past, showing them from before they were married to when they get on the plane. There are a few revelations in there, which help to explain their characters, and one which was very surprising, but overall it wasn't as great as the last couple of episodes. Hopefully they expand on their stories in the future.
There were also a few interesting advancements in other parts of the story. One was a division between the survivors, and the other had to do with Charlie and his drug addiction. The division story was interesting, but could have been more interesting. It might still be in future episodes, but so far it hasn't really been anything that great. The story with Carlie is more interesting, and helps to set up the next episode. It also strengthens John's role as a kind of spiritual leader for the people, showing them what the island can give them.