Let's get the flaws out of the way. It relies really heavily on the "Space is an Ocean" trope. It takes the submarine movie in space bit way to far to where apparently sound can travel through space. Translating other genres to sci-fi is an age old concept, but you need to stray from the source where appropriate.
Second is the internal conflict on the Enterprise. Styles is a guy we've never seen before and will never see again. He's supposed to be a bigot, but he's actually got a point, at first. If no one's seen a Romulan, how do you know they haven infiltrated the Federation? His focusing on Spock is a bit less forgivable, given his long Starfleet career and the fact that there's a planet full of Vulcans. However, while an earlier stardate, this episode actually originally aired a few weeks after "The Menagerie", so audiences at the time may have been more accepting of the idea of a Spock betrayal. Styles' attitude shift was a bit far-fetched, but not wholly unbelievable.
Now let's get to what makes this episode ooze with awesome. The chess match between Kirk and The Romulan commander was awesome. It was a match between equals, each with advantages and disadvantages to deal with. I somewhat disagree with another reviewer who called this a clear good guy vs. bad guy scenario. While the Romulans are certainly the aggressors, The Commander and The Centurian are portrayed quite sympathetically. They're not wholly comfortable with their mission, but are experienced soldiers doing as ordered. Mark Lenard did a great job bringing out a brilliant, but somewhat tired old soldier. He got to make a classic line at the end that is really sums up how you feel about his conflict with Kirk,
"CAPTAIN, I REGRET THAT WE MEET IN THIS WAY. YOU AND I ARE TWO OF A KIND. IN A DIFFERENT REALITY, I COULD HAVE CALLED YOU FRIEND."
It's entirely believable from what we've seen. For both Kirk and the Commander none of this was personal. There was no malice. Each was doing his duty and that forced them into a conflict where only one could survive.
Second is the internal conflict on the Enterprise. Styles is a guy we've never seen before and will never see again. He's supposed to be a bigot, but he's actually got a point, at first. If no one's seen a Romulan, how do you know they haven infiltrated the Federation? His focusing on Spock is a bit less forgivable, given his long Starfleet career and the fact that there's a planet full of Vulcans. However, while an earlier stardate, this episode actually originally aired a few weeks after "The Menagerie", so audiences at the time may have been more accepting of the idea of a Spock betrayal. Styles' attitude shift was a bit far-fetched, but not wholly unbelievable.
Now let's get to what makes this episode ooze with awesome. The chess match between Kirk and The Romulan commander was awesome. It was a match between equals, each with advantages and disadvantages to deal with. I somewhat disagree with another reviewer who called this a clear good guy vs. bad guy scenario. While the Romulans are certainly the aggressors, The Commander and The Centurian are portrayed quite sympathetically. They're not wholly comfortable with their mission, but are experienced soldiers doing as ordered. Mark Lenard did a great job bringing out a brilliant, but somewhat tired old soldier. He got to make a classic line at the end that is really sums up how you feel about his conflict with Kirk,
"CAPTAIN, I REGRET THAT WE MEET IN THIS WAY. YOU AND I ARE TWO OF A KIND. IN A DIFFERENT REALITY, I COULD HAVE CALLED YOU FRIEND."
It's entirely believable from what we've seen. For both Kirk and the Commander none of this was personal. There was no malice. Each was doing his duty and that forced them into a conflict where only one could survive.