In the first few minutes of this episode, I thought this might be a series classic. Kirk, Chekov and Uhura are whisked away from the Enterprise and become gladiatorial slaves. The first act is indeed full of promise.
Sadly, as the story goes on, it becomes a rather messy fare. By this point, the 'shine' was starting to come off of the series, with episodes feeling less polished and less pleasing to watch.
The plot itself isn't all that bad, but script-wise it certainly isn't one of the series' sharpest.
Apparently, Sulu was originally meant to feature in this episode in place of Chekov, but George Takei was busy filming 'The Green Berets' (released 1968) and unable to appear in this story; Takei has since said that he regrets this.
Anyway, Kirk might be held as a slave, but it's not long before he's putting the trademark romantic Kirk moves on his 'drill thrall' Shahna. He never misses a trick!
Back on the ship, there is some nice but slightly generic feeling dispute between Spock and McCoy (and Scotty thrown into the mix) as they argue where they should be looking for the missing trio.
The idea of captured crewmembers being forced to participate in gladiatorial bouts has a lot of promise, so it is a shame that it isn't really developed very well here, and at best feels like an average episode.
The episode isn't a complete flop – as I say, the first act is very good, and the plot has plenty of potential. The fight scenes themselves are well choreographed (Shatner was in good shape during the period), and the story does have its intriguing points.
This isn't bottom of the barrel – it is watchable and there would (sadly) be much worse to come; but the episode is let down by a shaky script, and comes of mostly feeling as a missed opportunity.