"Child's Play" is the Borg episode Voyager had been working toward since the third season, something it could almost do with Seven but not quite, the fullest exploitation of being in the Collective's home territory of the Delta Quadrant.
"Hope and Fear" had been pretty close to the mark earlier, but it's in "Child's Play" where the psychology of having the Borg in your backyard really hits home. Here we learn just how Icheb became assimilated in the first place, and it's pretty despicable, but at the same time almost understandable.
Here's a spoiler alert:
It's his parents who set him up for it, in the hope of crippling the Borg with a virus. Hey, Janeway does the same thing, several times, until it finally works.
It's a fascinating insight into the real effects of the Borg. If "Best of Both Worlds" had remained the definitive statement, that would have been fine, but short of finally discovering just how the Collective was formed in the first place, there's no more essential story to be told than more than just the trauma of assimilation, but how those who hear it on the news, so to say, actually react to it. It's like a War on Terror story told more than a year early. Like all those Deep Space Nine stories about the Bajoran Resistance, it's a continually relevant tale that the later Star Treks never really got credit for.
If "Child's Play" doesn't convince you that the sixth season of Voyager wasn't as worthless as you heard, then there's nothing else I can say.
But I'll keep trying!
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Memory Alpha summary.