I don't really understand why so many people praise this manga. It has good sides: art (it's genuinely gorgeous, author should really try to make some horror manga with that skill), world setting is pretty good, hell, stories of some of the supporting characters almost made me shed a tear. But, there's two big problems.
1) Remilia herself. She's perfect practically from every angle, she's beautiful, smart, physically and magically strong, diplomatic. There were moments were it was explained how she reached this level of perfection, but it all still feels really Mary Sue-ish. Not even once her plan gets derailed, she always succeeds on the first try while everyone praises her and practically worships earth underneath her soils. It just gets tiring at some point, to see everything go according to plan without any errors.
2) Pina or, well, transmigrator in her place. She feels like a cartoon villain at best and piece of cardboard with cutely hideous face at worst. Manga shows time and again how truly horrid she is, how she doesn't have any good in her. I didn't expect to see some explanation for why she's like this, I don't mind at all that Pina doesn't have some sob story to explain everything she's done, but damn, would it hurt to make her less of a collection of all the bad character traits they could think of?
Still, it's not the worst I've read, it certainly made a lot better than some other reverse villainess manga. If you read it without expecting too much it will be a nice read. Probably.