Tl;DR: Fab world building, well constructed characters, and a cause you can get behind. What more does a YA Fantasy really need? 
 Red Queen is a really solid read. I personally love me a cynical, headstrong MC, which is exactly what we get with Mare. She's determined to maintain any bit of agency she can in defiance of the oppressive Silver ruling elite, even once she is forced to live among them. She's the type of character we all like to imagine we would be if we lived in her world. But despite the tough appearances she puts on she is scared, confused, uncertain, and just desperate to do whatever she can to help her family and herself survive. 
 This is honestly a terrible comparison so I apologize in advance, but while I was reading I kept thinking that this book was everything The Selection Series could have been if it had only focused on the actually interesting parts of the story. Mare is forced to move to the royal palace to live among the Silvers and is forcibly betrothed to one of the Silver princes. Of course she slowly starts to wonder if all Silvers are terrible and a bit of romance ensues. But the primary focus is on the bigger picture: the growing anti-Silver sentiments and attacks and the rebellion attempting to overthrow an obviously oppressive institution. Also Mare is a way better MC but that is neither here nor there. 
 Because I know people will be wondering: yes there is a love triangle. With that said, it is handled in a very different way than your typical YA romance triangle and in a crazy twist of events actually adds a really interesting dynamic to the book. I liked it a lot. So if you normally avoid the love triangles, I'd strongly encourage you to whitelist this one. It does something pretty interesting with the trope. 
 This is one of those books that you give 4 stars to because it just wasn't quite screaming 5 stars at you, but you also can't really even say what it could have done better because it is a really solid read. Personally, I think this likely would have been a 5 star read for me if I hadn't been tipped off to a few things ahead of time (on a totally related note, be looking for an upcoming post on my blog about why I don't read/watch book reviews anymore.) Even though the exact details weren't spoiled, it was enough for me to easily guess a few of the plot points, and this book just really relies on you not being able to do that. For me 4 star reviews are for really excellent solid books and 5 star reviews are 4 star books that I have an extraordinarily good experience with. And unfortunately to no fault of its own, the experience bit was taken away from me a tad. *shrugs*