The original Star Trek television series, the show that kicked off a pop culture phenomenon, celebrates its 55th anniversary this year. While the series only ran for three seasons before its eventual cancellation in 1969, the show proved highly influential, packed with acclaimed episodes that posed deep questions to the crew as they delved into the unknown.
With that said, not every season maintains a consistent level of quality. Here is the definitive ranking of all three seasons of the original Star Trek series, including both highlight episodes for each season and some of the show's biggest disappointments.
3. Season 3
The third season of Star Trek is regarded by many, including the cast and crew themselves, as the weakest season in the original series. Dissatisfied with the new time slot given to the series by the network, series creator and executive producer Gene Roddenberry was associated with the production in name only, no longer personally reviewing and rewriting each episode's script. The production budget for the final season was also slashed, accounting for the noticeable drop in quality on a technical level.
Some highlights from Season 3 include episodes like "The Tholian Web" and "Let That Be Your Last Battlefield," but it also contains some of the absolute worst episodes of the entire series. Among the worst episodes of Season 3 -- and the series overall -- are "Spock's Brain" and "And the Children Shall Lead."
2. Season 1
The season that started it all, the inaugural season of Star Trek first introduced audiences to the Enterprise crew and its memorable characters in 1966. The nuances of Starfleet and the main characters are established, though the show overall is still visibly navigating its tone and in-universe rule as evidenced with clumsier Season 1 episodes, such as"The Conscience of the King," "Court Martial" and "The Alternative Factor."
That being said, the series shows a lot of its charm and promise right from the start, and the vast majority of Season 1 episodes are fantastic installments. Among the more notable episodes are "The Menagerie," "City on the Edge of Forever," which would both go on to win Hugo Awards, and "The Space Speed," an entry that would directly inform the franchise's second feature film, Star Trek II: The Wrath of Khan.
1. Season 2
While Season 1 laid the foundation, the original series' second season would maintain a more consistent level of quality throughout, while the cast and crew's dynamic would visibly gel on-screen. This allowed episodes to go deeper into the main characters' respective backstories and lean into the ensemble's strengths. The show also was able to introduce important pieces of the franchise's mythos in Season 2, from Vulcan culture in the season premiere "Amok Time" to the existence of the Mirror Universe in the episode "Mirror, Mirror."
Other high points of Season 2 include the diplomatic mission gone wrong in "Journey to Babel" and the more comedically leaning episode "The Trouble with Tribbles," as the show began to weave in more fun elements to the proceedings. Weaker episodes in Season 2 include the season finale "Assignment: Earth," which was intended as a failed backdoor pilot for a planned series by Roddenberry, and the garishly terrible episode "The Omega Glory," where Kirk saves the day by reciting the American Constitution.