As I read some of the reviews, it became crystal clear that many people just vote it down because its not what they expected. That's why I want to write about what people should expect.
Its a completely fictional story losely based on a 18th century, French setting a short time before the revolution took place. The series doesn't try to be historically accurate and it never pretends to be.
The story is in the supernatural, fantastic genre and there are recent, politically modern elements in it, like references to refugees and female gender roles, which at times can be a little bit plain and over the top. The characters are clearly split into the bad and the good guys, but even for the bad guys, there is some reasonable background story. There are worse and less elaborated character building series of this kind around.
The special effects are, for a series, very good, the cinematography and music is excellent, acting is not always on the highest level, but still very good and convincing, at worst solid, with attractive characters doing a good job for the storyline. In many ways the series reminds me of American movies from the 1990's and 2000's, just with more CGI well-placed where necessary.
Comparing the series to other gems of the genre, movies like Interview with the Vampire (1994), but especially Brotherhood of the Wolf, in French Le pacte des loups (2001) come to mind. Basically, its Le pacte des loups altered and transformed into an 8 episode series. All the basics and references are pretty much the same. So if you liked Interview of the Vampire, you might like this one, and if you liked Brotherhood of the Wolf, you have to love it.
People which don't like the fantasy and horror genre, but want to watch historically more accurate depictions of pre-revolutionary France, should go for other movies and series, or even better read actual historical books and scientific sources.