Okay, it\'s an alien who wants to observe good vs evil and already seems to be evil, which makes little sense. We see Lincoln (which actually starts as a nice idea and kudos to all for playing it straight) and Surak of Vulcan... they, with Kirk and Spock, are forced to battle 4 evil figures. 3 from Earth\'s past, and Kahless the Unforgettable (it\'s a riot how TNG and later spinoffs turn the guy from being an evil sleaze to a heartwarming guy with a melted candy bar glued to his forehead...)
But it\'s good versus evil with all the stereotypes within. Trek TOS always discussed human nature. But this story doesn\'t bother with any overlapping ideas. As a result it\'s trite and fairly obvious too.
But it\'s the straight-faced approach to Lincoln that makes it interesting... but it\'s also obvious the scene where \"Lincoln\" calls Uhura the N-word was hard to watch, even though it is plausible - that if Lincoln were alive and teleported 400 years into the future, he would likely say the n-word. Uhura\'s answer is a bold attempt to give hope for the future, and that context is one most people won\'t see today and, as with many elements of TOS, get overlooked because the context of the 1960s is long gone.