I think Plato's Stepchildren is underrated. The Dwarf Alexander is one of the most memorable guest stars in the series. His character was touching. The speech kirk gave about size, shape, and color not mattering in the federation was classic Roddenberry ideals.
I argue the only reason people dislike this episode is because of some of the silly stuff the characters are forced to do by the bad guys. That is only a small portion of the story and As it's supposed to be humiliating and degrading I think it's effective.
I agree completely. Michael Dunn is superb as Alexander. And the humiliations that Kirk and Spock are forced to endure are wrenching and disturbing to watch.
My only problem with the episode is that the use of kironide to induce telekinetic superpowers was never mentioned again. Though I guess that injecting heavy metals into your bloodstream would likely be toxic in the long term.