This book is also part comedy, with lots of silly Regency-era scrapes and escapes from same. Friday's has a lot more romance to it than Cotillion, but I actually much preferred Cotillion.
This is largely because I found the male protagonist in Friday's difficult to take, mainly because his treatment of the female protagonist for parts of the book is, by modern standards, abusive. He's not a monster by Regency standards, but he's described on multiple occasions as doing things like boxing her ears and shaking her violently. It's the kind of minor violence that was common during the time period but it's squicky to read about it now. The emotional relationship is also rocky: much of the book's tension comes from the female protagonist making some social gaffe that she was understandably unaware of, and the male protagonist exploding at her until he realizes it's not actually her fault she wasn't taught all this as a young girl.
In fairness to the story, the male protagonist does eventually figure out that he's a jerk and has been treating her badly, and the resolution suggests he'll do better going forward. Still. At one point the female protagonist is being pursued by a very nice man who loves her quirky ways and doesn't want her to change. I found myself sorry that it wasn't feasible in the setting for her to ditch the male protagonist in favor of this guy, who really deserved her more.
The other thing that bugged me is there's a lot of terrible "romantic advice" in it, stuff about playing hard to get and suchlike that reminded me of books like The Game and The Rules. In fairness, the protagonists were usually repulsed by this advice and had to be tricked into it by their friends, but the way it ... kind of ... works and the semi-endorsement of such manipulative tactics was ick.
This aside, the book has many good points. The supporting cast was entertaining, well-meaning, and generally likeable. There's lots of funny bits. The protagonists get along well for a substantial chunk of the book, some times because they are both tripping merrily along the same foolhardy path, but it's still amusing to read. Some of the romantic parts are genuinely touching, especially one point where the male protagonist says he'll give up the female protagonist so she can be happy with her more-deserving suitor.
I'll give it a 7, and will read more Heyer later. For now, I'll take a break from Regency romance: it really is a crapsack world, and modern Regency novels keep reminding me of that. (Austen rarely does. I don't know why that is.)