This was still pretty dang good although I didn't like it as much as its predecessor. It covered much of the same territory, although in a slightly different style. Instead of a country house mystery of the 40's it was a spy thriller of the 40's. So if I hadn't read Farthing I might have liked Ha'penny more. Or maybe not, since of the two I actually like country house mysteries slightly better. But mainly it was an issue of not enough new. Since I already knew the place and some of the people, I was less impressed by the seamlessness of the joins between the real and the alternate history. Although the mix is just as good as it was in the earlier book.
Also since there's a third book I was pretty certain that this one wasn't going to resolve the major questions, which meant that I already had a pretty good idea of what likely was and was not going to happen. So that reduced my enjoyment too. But its still well written, with believable characters and interesting ideas subtly explored.