I’m in the process of a TOS rewatch right now, on S3. I feel like I’m slowing down because I don’t want to reach the end again.
Shatner’s performance as Kirk is just pure fun to watch. His delivery is confident and over-dramatic, and it’s like he’s competing with the main cast and even the guest star actresses to always be the prettiest one in the scene, lol. He gets a lot of flak for his “main character energy” on and off the set, but he sort of is the main character, and he also really embraced engaging with the (extremely passionate and opinionated) fans over the years, which I appreciate. I don’t think any of them were prepared for the level of popularity they were thrust into (still household names nearly 60 years later!), and many of them didn’t know how to handle it.
Kirk is a cocky tomcat. Spock is a prissy black cat that doesn’t like change. McCoy is a stray that wandered in from outside, but seems to be friendly most of the time.