I was going back and forth with 3.3 and 3.4, since this is a clichéd story (even for its time, I think) but a good dramatic story that is usual for the 1st season. So, I give it a 3.35. The overall pacing is slower, more dramatic than later seasons
Corbomite is magnificent. I hate the last ~3 mins; but up until then it is absolutely magnificent. Crackles with energy. The sharp dialogue on the bridge is amazing.
Best are the moments of dialogue leading directly up to Kirk's idea for his gamble. Kirk flailing around for an idea; Spock's failure to produce a viable recommendation; the Chess metaphor; McCoy's heated rebuke; the way the argument produces the key word; the look on McCoy's face, like he just swallowed a lemon, when the alien intones "You now have three minutes" and McCoy realizes that Kirk has bigger things to worry about right at that moment. It might be the best dialogue writing in the show, in the specific sense of having the things characters say
actually drive the plot. The words themselves key the next action in the story – and the next action itself, Kirk's bluff, is in fact words! Just words. Later Scotty & Spock engage in some byplay, that seems like they are self-consciously trying to relax the junior officers.
Of any scene in Star Trek, this is the scene that most evokes the early 60s (and late 50s) tradition of sharp dialogue writing for TV. They moved away from the need for that. This was the first bottle show – the next one, Balance of Terror, still had some inter-character tension on the bridge. But the series moved more toward visiting other planets and having guest stars drive the story conflict.
One of my favorites. I wish, I wish the ending were stronger. But the main body of the episode is so terrific, even a weak ending can't undermine it too badly.