With more historical figures than a junior high school history pageant and the most comically obvious trap ever laid for our heroes ("Help me, Spock!"), this planet-based Gene Roddenberry "good versus evil" story is one of the more memorable TOS episodes, despite not being very good.
Like a precursor to Super Friends, Kirk and Spock get to fight alongside their heroes, Abraham Lincoln and Surak, against four of history's most evil villains, though sadly the latter doesn't include Khan. (Hitler is excluded as well, but that's probably for the best).
If the episode has a strength, it lies in the talents of the character actors, with Lee Bergere particularly believable as Lincoln. (Phillip Pine is also somewhat interesting as the fictional Colonel Green). But the story takes a meandering path to get to its point, and it's not a very interesting point at that. (As a morality play wannabe, the episode really needs evil to lose due its own internal destructive nature, but the writers choose a different climax). And as an action-base episode, it doesn't help that the fighting is confined to the small planet stage set, reducing what should be an epic battle to minor skirmishes.
It's likely Roddenberry new this one wasn't working out very well when he was writing it, which is why he ultimately gave up on it. Unfortunately, producer Fred Freiberger pulled it out of the trash and gave it to Arthur "Way to Eden" Heinemann to finish.
The Klingon guru Kahless, played by a different actor, returns in TNG's sixth season episode "Rightful Heir". The Vulcan guru Surak, also played by a different actor, returns in ENT's fourth season episode "Awakening".
There's not much of note here, other than new shots of the Enterprise and the planet (replacing the original's reuse of Vulcan). The new planet sphere, however, is one of the best this project has accomplished, a vivid globe of hot magma that ties nicely into the surface environment. The digital team also touches up Lincoln's first appearance (in space), redoing the surrounding stars.