Brief "Lost" spoilers coming right up...
In isolation, "One of Us" was a perfectly okay episode. The flashbacks told us new information, fit seamlessly into the teaser from the season premiere (complete with an explanation for Ben getting kicked out of the book club, still the funniest line of the season), did a good job of explaining Juliet's transformation from the woman she was in Miami to who/what she became, and was in general a good showcase for the versatile Elizabeth Mitchell.
But I'm suffering a severe case of Others Fatigue, which, coupled with Jack being his usual obtuse, gullible self, makes it hard for me to get too enthusiastic that, at its heart, is just another one of Ben's mindgames, even if it brought back Goodwin for five minutes.
Your mileage may have varied.