Wow - this episode had me gripped. Firstly the concept was just great. Its been done before, but the intensity of the acting by Data and Troi simply leaves no room for breath.
Providing a slight hope of finding that these beings are the crew of a long lost starship added to the stress levels as I found myself hoping that Picard and the crew could liberate the lost souls of the USS Essex. The situation created by having Worf and Data matching up also added an extra level of conflict. It would have been good to see them battle for a brief fight, just to see Worf get aggravated even more.
I just love the way Data can say Picard and his voice oozes distain. Even though we know that the crew is still going to win the day - the ending seemed to tail off too quickly, with a real lack of a final twist to the event. That was my only disappointment though.