My biggest complaint about the first book was that I didn't find the main character, Flavia de Luce, very believable as an 11 year old. I found her much more believable in this book (despite her precocious chemistry knowledge, especially with respect to poisons). In fact, I found all of the characters to be better drawn in this book - the older sisters, Ophelia (Feely) and Daphne (Daffy) are much more rounded rather than being purely evil; and most of the secondary characters seem realistic rather than just caricatures.
But unfortunately, the story doesn't hold up as well this time around. There are two mysteries to be solved that (of course) are linked together - a young boy died 6 years ago; then a visiting puppeteer dies in the middle of a performance in the "present" time (the book is set in 1950). While it was fun getting to know the characters, Flavia solves the mysteries mainly by collecting gossip from different villagers, without any excitement or true deduction. A bit like an 11-year-old Miss Marple.
There is a third book in the series due out next year - A Red Herring Without Mustard (the author seems to be into quirky titles!). As before, I will probably read it, but will either check it out of the library or wait for it to come out in paperback.