Threshold is an attempt at remaking The Fly (mostly the Cronenberg version.) Even though it's a valiant attempt at body horror, the limitations of network TV really prevent it from reaching its full potential. From the same era, I'd say The X-files did that sort of thing better.
And in fact, the reset button ending is what completely neuters Threshold. The ending to Cronenberg's The Fly is really powerful because of the final pathos and irreversibility. Instead of leaning on this, Threshold just goes incomprehensibly weird.
I think Star Trek's most successful body horror episode is probably TNG's Genesis (though I think Enterprise might have had a couple valiant attempts I should try to remember.). Genesis also suffers a little from its reset button, but since it doesn't lean on pathos like Threshold and The Fly, the reset isn't as annoying.
But in general I really feel like Star Trek should now be able to do good episodic TV which still shows real character progression and avoids total reset buttons. Some recent series leaned too far into serialization, but I'm hoping SNW strikes a good balance.
People with freckles tend to avoid sunlight, yeah.