Not TREK's finest hour, "Gamesters of Triskelion" mines the sort of storyline that would have fitted better into Lost in Space than in STTOS. It would get worse in the final few episodes of Series 2 (and I will gert to those in due course) but really - Kirk and crew as slaves in a gladiatorial arena is a bit of a low point.
The only this that makes this stand out in most Trekkies minds is the appearance of Angelique Pettyjohn as a fighting femme - though when TREK fans want to cite examples of bad TREK, they'll often allude to "alien girls in silver bikinis". That'll be our Angelique, then!
So - a bit of a space-filler ... but not as bad as "A Piece of the Action"