I like Heyer's Regency romances rather a lot. That said, if this had been the first one I'd read I'm not sure I would have gone on to read any more of them.
The trouble is, this book tries to be both a Regency romance and a detailed fictional depiction of the battle of Waterloo and falls squarely between two stools in doing so. I enjoyed much of the romance itself, but felt it could have been carried off without quite such a detailed account of the battle, which seemed shoehorned in to some extent. And if it was an account of the battle she wanted to write, it might have been better to do it without the romance appended. The whole thing seemed like two books which had had a head=on collision and inelegantly merged their contents.
Not a horrendously bad book - the writing itself is still eminently readable - but not Heyer's best by any means.