There are so many reasons "Tin Man" should have been a winner of an episode. Instead, it's almost like the Next Generation adventure Sheldon Cooper from The Big Bang Theory would have actually experienced, a little like the disappointment he discovered when he met "Wesley Crusher" for the first time.
The ending is a good beginning. It attempts to shape "Tin Man" into a Next Generation version of The Motion Picture, as Data describes it. And that's basically how I remember it, too, when I think about it that way. The way Decker merges with V'ger in the first Star Trek movie is exactly like what happens to the Betazoid and the Weird Space Creature. (There are a lot of Weird Space Creatures in Star Trek.)
That last line features just one of the element misfires of the episode, the fact that the guest character who all but completely dominates the episode and thus saps its energy with his depressive outlook, is barely relevant to Troi. She knew him. She's as close as he comes to thawing. Otherwise he rubs everyone the wrong way. He dismisses Data until they're forced to work together. That's all well and good, but it certainly doesn't work as a Data episode, because it isn't. The focus is always on the guest character.
The other way it fails is in the way the episode begins, which is on another seemingly strong main character note, this one with Riker. Riker had the most interesting pre-Enterprise career of all Picard's officers. Until Deep Space Nine, however, most of the time when Star Trek referenced a character's service prior to the start of their respective series, it was handled poorly. Ironically, Riker ended up being one of the few who got it right (along with O'Brien in "The Wounded") with "The Pegasus" from the final season (and of course Picard in "Tapestry"). Here is a particularly botched opportunity. Such a strong emphasis early on only to amount to nothing at all. Then again, the series tried so hard to emphasize Riker's career, and almost always got it wrong. This is no exception in that regard.
One more wasted element is the inclusion of the Romulans in their last real outing of the season. After far more significant moments previously, they go out with a whimper.
It's not a bad episode, it's just tonally and conceptually off-center. Both problems could have been avoided by sticking with Troi and Riker as they were presented as relevant, rather than abruptly shifting to Data. It would have been a great opportunity to lightly explore Troi and Riker, too. Generally a missed opportunity and probably the worst episode of the season for it.
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