"Paradise" shows us Spock's human side in a story which questions what we think defines happiness. Those spores seem so benign - unlike the alien plants Leonard Nimoy would encounter a decade later in Invasion of the Body Snatchers - and Kirk is so dead set against them. He's right about paradise being not what man was meant for, but the tragedy is, it gives Spock the opportunity to feel, without his emotions spilling out of control. The conflict makes for great drama. In "Babel," we meet Sarek and Amanda, and discover the roots of the estrangement between Spock and his father, a relationship that would be explored further throughout the show and the movies.
Fontana also co-wrote the TNG pilot, "Encounter at Farpoint." It may seem a bit rough around the edges now, since the cast was so new and different, but it holds up. Omnipotent beings are a Trek tradition, and Q differs from the others in his flippant attitude and his eagerness to challenge humanity's progress as a species and their right to the stars.
Some of Fontana's scripts, like those of other writers, were rewritten by Gene Roddenberry. Fortunately, her vital contributions to Trek lore are known and have been recognized. As a woman writer, this is doubly important, because sometimes she used male pseudonyms. By any measure, Fontana was a pioneer.