I wasn't there for it, but it was a surprise all right. Denise Crosby's voice was recognizable in her previous "shadowed" appearances, but it was so bizarre to think she might be back that the close of this episode was still shocking. (For TV-only fans, that is. The news that she would be in the episode had broken a while earlier, so those who followed the magazines and whatnot knew about it.)
Of course, the question of who she was playing
kept people guessing all summer. Tim Lynch was reviewing TNG on Usenet at the time, and in his review of "The Mind's Eye" he remarks that when we find out the truth, "we can finally, FINALLY, lay to rest all of this 'daughter of the Ent-C Tasha' nonsense."
Definitely one of Trek's better cliffhangers. I was so disillusioned when I found out that TV writers don't necessarily know
how they're going to resolve these things... Michael Piller, for instance, hadn't decided how to end "Best of Both Worlds" until just before the deadline.