Ultimately an interesting idea that gets a bit too weighed down by technobabble, and a little bit too much forcing of the plot towards where the writers wanted to be with the ending. And nothing felt particularly new either – unaware duplicates have been done better before (*Whispers* in DS9, most recently).
There was some good character development (perhaps it was more character punctuated equilibrium) from Harry Kim, at long last. But beyond that the episode struggled under a lot of exposition, and several implausible turns.
(Why I love Tuvok: he correctly talks about the “Ensigns Kim”, rather than “Ensign Kims”).
526 down, 211 to go.