If you have not read Cinder you need to go do that. If the words sci-fi Cinderella retelling don't make you want to read it maybe my review will. Either way if you have not read Cinder I am warning you that this review will contain spoilers for Cinder, not for Scarlet just Cinder.
Scarlet was just as good as Cinder. A lot of the time second books tend to drag and not be nearly as good as the first book. But Scarlet does not fall into that trap. Maybe it is the introduction of a new POV or maybe it is the added cast of characters, but Scarlet manages to stay fresh where others fail.
In case you could not figure it out, Scarlet is a retelling of Little Red Riding Hood. A retelling that will blow your mind with how different it is from the source material. It takes place in the same world as Cinder just in a different country. Scarlet is just as sassy as Cinder but they are different she is less insecure and even more kick-ass if you can believe it. If you fell in love with Cinder then you will like Scarlet. She is sassy and I swear I want her red hoodie.
There are also some other new characters such as Wolf who is not all he seems, and Thorne who I thought was going to be annoying but I really liked getting to know. And don't fret, there are still some of your favorite characters from Cinder such as Iko, Queen Levana (though if you like her *side eye*) and of course Kai.
The two stories of Scarlet and Wolf looking for her grandmother and Cinder trying to escape Queen Levana may seem like they would not come together but they fall in place perfectly and are told through alternating chapters interspersed with chapters about Kai.
Basically if you liked Cinder get ready for even more fun in Scarlet. Also while some questions are answered you will be joined with me in wanting Cress which does not come out till next year.