There are two fairly significant reasons to take "The Changeling" more seriously than your probable lack of any real memory of it would suggest:
1) It's the template for The Motion Picture.
2) It's an Uhura episode.
No, really. It's an Uhura episode. It's pretty much the only Uhura episode, so if that's pretty important to you, "The Changeling" is probably pretty important, too. It's not heavily an Uhura episode, but it features her more significantly than any other one. The probe wipes her memory, and she needs to have it reprogrammed. That's it, really, but it's still the most significant thing, other than kissing Kirk, that happens to her in any episode.
Personally, I would've loved for that whole business to have been handled differently. In later eras, it would have been. But in this series it is what it is. It does suck that her big spotlight is having her memory wiped, and getting it back isn't the whole focus of the episode. That would certainly have been interesting.
The episode quickly reverts to the same story featured in Motion Picture, and that's all you really need to know. All of this means that you can certainly enjoy "Changeling" for these elements, but it's not as awesome as you might hope. It's perhaps the only time you'll want to just watch the first movie instead (with Uhura being replaced by Ilia).
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