A good thriller requires a good villain, and "Space Seed" has Khan Noonian Singh (Ricardo Montalban), a 20th-century tyrannical leader from the era of the Eugenics War—a conflict fought over the dispute of genetically engineering human beings. Khan and his crew have been in suspended animation on the S.S. Botany Bay since 1996. Now awakened, Khan intends to reinitiate his old ways, beginning with taking over the Enterprise and (as they say) moving on to the rest of the universe.
Khan's quite a presence; his skill in manipulating historical officer Lt. Marla McGivers (Madlyn Rhue) demonstrates his great ability for balancing attractive charisma and frightening psychological terrorism—and Montalban is exceptional in the role. Khan's tactic in trying to force support from crew members (subjection to suffocation) is particularly treacherous.
The ending fight scene was a little typical in its way of "Kirk versus an adversary," but it was executed well. Oh, and there was great use of Bones' attitude in the early scenes ("Well, either choke me or cut my throat—make up your mind!"). But like much of classic Trek, the polemics linger: the argument and implications of "improving man"; the reflection upon a savage reign of tyranny; the savageness inherent in humanity. All interesting stuff.