Julius Norreys has to be one of my favorite dandies in fiction, probably right next to Julian Kestrel from Cut to the Quick of the late (great) Kate Ross. And Julius has some thought behind him as well, this is no plug-and-play period-piece dandy. What makes a man adopt the fashion of well, caring about fashion? Why does anyone pride himself in knowing more about buttons than anyone else in London? There's a reason he dresses the way he does, and you're going to learn it.
Harry, also, is a very well-developed character, struggling with his profoundly casual morality and a fondness for not being poor, and where he can fit himself in between his late parents' revolutionary zeal and the cruelty of the British aristocracy in the height of the Peterloo Massacre. Add in the fact that he's depicted as bisexual with zero fuss, and the only woman character in the book is portrayed as a real person and not a 2D generic girl-villain, and you've got a tightly bound romance standing head and shoulders above just about anyone else.
The sex scenes are also amazing for the simple reason that the characters keep their personalities during sex. Sex scenes can get kinda generic as we all know, the what goes where and people feel the things, etc etc, but this is decidedly not generic magic romance book sex. Julius is prickly and distant during sex. Harry is cheery and giving. Eventually they figure it out, but their sex is an extension of them, not something that occurs besides the other things they are.
Certainly stands up to a re-read!