Intense episode about a shuttle craft mission lead by Spock that crash lands on a most unpleasant world. Indeed, the dangers posed by it's hostile environment leads to a near equally hostile landing party as Spock finds his leadership abilities called into question. It's been well explored how the Vulcan's logical approach to the crisis proves ineffective in dealing with the stressed-out humans under his command. The only thing to add might be that,at times, Spock does display an almost human surliness that seems very un-Vulcan. But, since this was a first season episode, it may have been filmed before Leonard Nimoy had fully come to understand his character and the proper way to play him, (for example, he was still speaking with that put-on British accent like when he pronounces command as "cuh-mawnd"). Clearly, this is not the more controlled Mr. Spock we would see in later episodes like "The Doomsday Machine", but it's still a good performance and the script provides an interesting set of problems to watch the usually unflappable character struggle to deal with.
As if crash landing wasn't bad enough, the primates that live on the planet are a neat addition to further complicate Spock's bad day. Not so much seen as glimpsed (and a wise move, too as the only one shown up close looks like it's wearing a fur dress), these hairy monsters prowl about in the fog making hissing noises and bellowing roars. They attack with huge spears, and in one scene a comparatively tiny human is mauled to death. Thoroughly nasty, their presence in the story leads to a neat scene on the Enterprise bridge as Kirk hears the report of a returning search party leader: appearing on a viewer screen all bruised up in a torn-up uniform, Lt. Commander Kelowitz tells Kirk how his team was attacked by "creatures similar to ones discovered on Hanson's Planet, only much, much bigger. Ten- maybe twelve feet in height." Clearly exhausted and maybe a touch traumatized, Kelowitz cautions Kirk that if the missing shuttle craft crew are on that planet, but doesn't have to finish the sentence for Kirk to get his meaning. It's an effective little touch that casts a shadow of dread on the possible fate of Kirk's missing crew members. In fact, they should have used this seldom seen character of Kelowitz more often as he would have made a great running bit. Like Scotty's dire warnings about the condition of the ship's engines, or those red shirted security men who were always first to bite the dust, you'd know the situation was dire if Kelowitz showed up with another alarming report for Kirk.