Well, the first reason why I even decided to watch this show was the Victorian aesthetic which I received in great quantity. Even though the whole story is built around an imaginative country in Europe, its culture and history were written incredibly well and believably, especially the occultist side of it, which was inspired by its actual rise during African colonisation. But the setting is not the only appealing part of Gosick.
First of all, this is a detective story which contains really well-constructed cases as well as some wack and obvious ones which are more like proto-cases before the main one in the story arc. The best thing about the detective part of the show is that it is not there just for fun, but to better tell the story of the country since pretty much every one of them is somewhat connected.
Secondly, Gosick's characters are actually pretty cool. The cast is not so diverse, but memorable nevertheless. The best one is for sure Victorique de Blois, but others like Cordelia, Kujou, Grevil, Brayan Roscoe, Cecil and others have their moments too. I can say that the Light Novel has done a better job at flashing them out, but that's unfortunately not a rarity.
And last, but not least is the atmosphere, this point is directly connected to the setting of the show, but one thing that intensifies everything about it is the music! From the masterpiece of the endings to pipe organ compositions, Gosicks ost is truly magnificent and for some reason, not a lot of people point it out.
That's gonna be it, I think I wrote a bit too much, but this is unsurprising, considering Gosick is one of the shows that I will not shut the fuck about. Anyways, I hope I made a good job at selling it!