In case you forgot: Kirk sends the Enterprise into THE NEUTRAL ZONE!!! despite it being, well, the Neutral Zone. Next thing you know he's aboard a Romulan vessel, but it's okay! That was the plan all along! With Spock's help Kirk steals the Romulan cloaking device, as per the Federation's orders.
There is all kinds of intrigue going on in this episode, and it keeps you in suspense for a good long while. Could our favorite starship captain have finally lost it? Of course not, no, but when it aired there was no telling it might be an attempt at an out for Shatner. The plan is a relatively complex one, all things considered: Kirk has to feign illness long enough to convince his crew there's something really wrong, then he has to hope to get captured by the Romulans instead of just blown out of space, then he has to find and steal a piece of alien technology (preferably without getting caught). I guess the idea that the Federation would risk what may be Starfleet's best Constiution-class ship on such a dangerous stealth mission is a bit hard to swallow, but maybe they figured that out of all Starfleet, Kirk would be the best man for the job. He's certainly Starfleet's biggest ham.
The bad: Spock's little tête-à-tête with the Romulan commander is a bit much; I was hoping she would remain a stoic, ambitious, smart starship commander but no. Sigh.