It's being hailed as a "Harry Potter" for adults. This strikes me, and people who have read the book already, as a marketing ploy. Granted it is about magic as a gentlemen's scholarly pursuit in early 19th century England, but it reads as a homage to, and slight parody of, British social comedy novels. I've enjoyed the Harry Potter books but I'm not a nut about them. I generally eschew historical novels along with fantasy and/or sci-fi but I'm digging this book so far. I'll have more to say as I continue.
Side note: As a person who grew up with comics and the Sandman saga, it always amazes me the reverence our culture has for Neil Gaiman. The way Sandman was able to hit a massive audience was probably one of the high-water marks for DC Comics. There are only two back quotes to this book and one of them by Gaiman. He never does quotes, and this one is huge and imposing ("best English novel in seventy years…."). So if you like Gaiman at least check this out. It's on the Long List for the Booker Prize as well.