There's not a lot of love for episode on this site, perhaps because people want their sci fi to be timeless. The sixties are very much present in this episode, notably in the Barbarella costumes and characters. Others might find the story a bit simple. Yes, this is one of those instalments that give William Shatner the opportunity to be the action hero, and he clearly enjoys it. Like in some weaker episodes (and film versions) Kirk comes up with a rather obvious solution to his dilemma, just before time runs out.
But I think you shouldn't only accept and enjoy the flavour (and innocence) of the sixties, there are some things to admire if you see the episode in its context. Lieutenant Uhura gets picked for the small away team, which is remarkable on its own. (The series never really explained what Uhura's area of expertise was. Linguistics? Alien culture?) As the story unfolds, slavery appears to be a theme. Having Uhura there must create a link with not only the painful history of African Americans but also with the civil rights movement that had just reached its peak. (This episode aired at a time when optimism was running high, three months before Martin Luther King was assassinated.) The link is not particularly stressed, but it must have been poignant and daring for a prime time entertainment show of its time.