I thought it was an awesome eppy.A superior episode that avoided one of the problems that have tripped up some Lost eps: uneven layers. Basically, a lot of episodes have scenes you want to see, then either bad/annoying stories or filler scenes. I don't think a single flashback was wasted, the dueling storylines were balanced well between Jin/Sun/Sayid and Kate/Sawyer. They resolved each side pretty well while keeping consistant with the themes.
The flashbacks were very good, they had action, storyline progression (one option for Sun's child...), and showed a great side of Jin IMO.
Well, the end scene made this episode from a 7 or 8 to a nine for me. Seriously, what an AWESOME ending. WOW!