Wow, wonderful execution of the dream sequences! If I had to point to one episode this season that impressed me the most, it would be "Echoes." While it doesn't reach the level of Tony Soprano dream sequence episodes, it effectively spends a huge portion of the episode inside Alex's mind, as we explore her feelings about Division, Nikita, her childhood, and finally her great fear--the future Alex who has taken her father's place.
Meanwhile, Michael, using overpowered technology, find out that Alex was not in her apartment during a phone call, and was actually in the same room Nikita was in years ago after she had supposedly killed someone. The episode ends on a great cliffhanger, Michael sitting in a chair in Nikita's loft.
Those who've watched the La Femme Nikita series (and if you haven't, stop reading or you'll be spoiled) will probably recognize the similarity between Alex taking her father's mantle and Nikita, in LFN, being groomed by her mother to become head of Division.