Fairest is actually a prequel, but I wouldn't recommend reading it before the other volumes - it really lives within the context of the series, and you might not get all the information and hidden hints if you go into it blind. With that said, it is an absolutely gorgeous, fascinating piece and a full story on its own.
More importantly, it is a teachable example of how to handle fairy tales well.
Marissa Meyer goes above and beyond most fairy tale adaptations the market is flooded with. She doesn't only take a plot and some iconic images to go with it - a girl in a red hoodie jogging in a park, for example (*cough*Grimm*cough*) - but demonstrates a deeper, more subtle, and more graceful understanding on what stories are, and how they work. She conjures imagery that is both iconic to the sci-fi world she created, and at the same time evokes much older, almost indescribable dream-like memories we are all very familiar with from childhood. Sour apple candies. A pregnant seamstress with an embroidery frame in her hand. Blood on white sheets. Elaborate dresses for a ball.
The Lunar Chronicles series is an endless stream of Easter eggs for storytellers and story-lovers, without ever becoming too obvious or on-the-nose the way many adaptations are ("Get it? Get it? GET IT YET?! *cough*OnceUponATime*cough*), and even if you don't get any of them, it is still a great story on its own. It works with motifs, symbols and tropes, not entire pre-made folktale types. It plays with expectations, imagery, and plot in a way that walks the tightrope between familiar and intriguing expertly and with elegance.
Another thing I like about Meyer's writing: She, unlike many other YA authors, is not obsessed with the physical descriptions of her characters. No one is "gorgeous" and "chiseled" and we don't have to read doting repeat descriptions of the protagonists "golden eyes" (*cough*MortalInstruments*cough) - unless they are directly relevant to the story itself. She doesn't fawn over the looks of her characters - much like with the fairy tale elements, she gives you subtle hints, and allows you to dream up the rest. She works with more complex and open ideas of what beauty is, and presents a wide range of diverse looks in terms of hair, eyes, and skin coloring - and my favorite part: Her "Snow White" is not white at all.
Five stars out of five, and go read the entire series!