The idea - wow.. it was great. It did not gave us so much for the storyline, than was a lovely look back, giving us another way things may have happened and then enlightened us more the way Ancients were and what happened before Atlantis was left.
I do not know how to say it, but this episode - it really had the magic, catching storyline and the excitement. First of course, to know the alternative actions but just as a story - it was catching. And all the dilemma of time traveling and how one reality and actions there influence another. Great episode.