Meyer plays with traditional fairy tales and spins them in new, interesting ways. Her books are set in a futuristic sci-fi world where life is established on Earth's moon (where the Lunars, who have varying degrees of mind manipulation powers, reside) as well as still on Earth (with the "Earthen Union", which is enjoying a long era of peaceful coexistence). As you might guess from the title of the first novel, Cinder plays with the Cinderella fairy tale, and in this telling, Cinder is a cyborg teen mechanic who is quite out of place on Earth. She does have some of the same traits as Cinderella--she's a misfit whose stepmother and one of her stepsisters are both totally evil to her, and she does in fact meet a prince.
What I love most about the series is the way each new novel integrates new characters that weave into the storyline and add more dimension to the plot. The second novel focuses on Scarlet, who might bring to mind some of the traits of Little Red Riding Hood, and the third focuses on Cress, who echoes the tale of Rapunzel. Fairest is more of a companion piece than the others, and it focuses on the Lunar queen, who harkens back to the evil queen in Snow White. (I read this one after I finished Winter, and I'm glad I read them in that order.) Finally, Winter tells the story of Princess Winter, who certainly connects to character traits of Snow White herself. I feel the need to say that I don't often enjoy twisted fairy tales or things of that style, but these novels, with their sci-fi and fantasy elements and powerful, complex characters, greatly appeal to me.
In the classroom: These novels would be a great way to talk about diplomacy, the tradition of rule by bloodline rights, and the aspects of equity and fairness (as they relate to cyborgs on Earth who are treated as inferior OR "shells" on Lunar who are treated horribly). With biowarfare and other brutal military tactics, the lengths that regimes will go to in order to gain power certainly speak to what we see in our own world.
In lit circles: These novels would work great with other novels that build on fairy tales. Here's a nice list of YA books that relate to fairy tales provided by GoodReads.com. This series would also work well with other novels that focus on diplomatic relations, and they'd be a great complement to other novels with dystopian tropes (such as the Legend series by Marie Lu, the Graceling Realm series by Kristin Cashore, or the Divergent series by Veronica Roth). While Cinder would be the easiest to work with as a single work in the classroom, you could probably teach any novel in the series (they fill in gaps quite well and could stand alone).
I love Marissa Meyer (a successful NaNoWriMo novelist!), and I've thoroughly enjoyed the series. As a series, it's accessible, compelling, and fun while having enough depth and complexity to make it worth the read. I look forward to seeing what she comes out with next!