A Space Western. It very much was. Watching it in reruns out of sequence, it was difficult to know that Grace Lee Whitney, who played Yoeman Janice Rance, was originally slated as the female lead in the show with a higher rank. She was intended to be like a space exploring Miss Kitty with an understood relationship with Kirk. Shortly in to production, producer Gene Roddenberry ditched her very crudely in favor of his girlfriend, Majel Barrett (Nurse Chapel and the voice of the ship's computer), and his mistress, Nichelle Nichols (Lt. Uhura).
The absence of a true female lead also allowed Roddenberry to abuse his authority with the casting catch. I am no feminist supporter but Roddenberry was a pig, and he hurt the longevity of the show. In retrospect, there should have been more of Grace Whitney on Star Trek. She was beautiful, elegant and classy. She deserved better than what Roddenberry did to her, and how realistic was it that Kirk kept falling in love with aliens with presumably different anatomy than a human female?
To me it was more than just a space western. I like Star Trek's futuristic takes on real navy historical events.
Like dealing with an enemy who can cloak and the Enterprise crew saying it's unfair...always made me think about the Allies fighting the German U-boats in WW1. Or when some of them are captured and send a message encoded in some way that only the Starfleet folks can know it's there -- reminds me of the real life Captain Bainbridge of the USS Philadelphia in the early 19th century. The times they have to chose to destroy a federation ship to keep it from being used by the enemy reminds me of Stephen Decatur's crew from a real ship named Enterprise having to burn the Philadelphia. And in one of the Next Generation episodes (I think the one where Picard becomes a Borg) the Enterprise shows up for a battle too late and the crew spends a minute staring in awe of the death and destruction. That scene always makes me wonder what it was like for the real crew on the WW2 Enterprise to arrive at Pearl Harbor too late. (A scene I'm glad they put in the new Midway movie.)