it appears to be a concensus here
garf: Why do you think I'm a trekkie? True, I've watched almost all of the ST:TNG (not that many Voyagers, and even fewer DS9s), but I'm not a trekkie in true meaning of the word...
anyhoo, it's been so long since I've seen ST:TNG that I can't remember what my favourite episode is anymore..
however, there is one episode of Voyager which sticks to my mind:
In this episode, the crew just starts, well, melting basically.
Near the end of the episode, you find out that through something or the other (deflector dish and Tachyon beams were surely involved
the voyager was actually duplicated years ago, and these guys we've been watching for 50 minutes now are 'fakes'. However, they have real memories and real feelings, and they've had real experiences during those separate years that nobody else has had. They try to heal themselves, when that turns out to be impossible, they try desperately to send a signal or a probe which would spell out what happened to them and knowledge they collected, but in the end they fail miserably, all traces of them dissapear, only floating blobs in space...
it is so *perfectly* depressing, and completely out of tone with usual "we'll solve any problem in 40 minutes + commercials with a deflector dish and some tetrion beams" attitude, that it really, really sticks to my mind... I swear, the feeling of despair, sorrow and pure misery one feels at the end, simply because it is so UNEXPECTED -- you always expect a happy ending in Star Trek... pure genius
easily the most emotional and surprising of all episodes I've seen