These are by no means bad, but they're not as good as the first book in the series. The author never really earns the right to use the soapsuds trick as extensively as she does in these books; when it comes in at the end of the first book, it works on a temporary basis, but for it to be used this much, I'd expect some stronger limitations, or at least a better explanation, neither of which happen. More importantly, I was frustrated by the way Cimorene's character is dumbed down in the middle two books, apparently in order to give the newer characters a chance to shine. That said, book 4 is the second-best of the series, so it does end on an upswing.
Very charming and delightful. I love books that take on fairy tales with a feminist sensibility, and this is a very good example of that genre. The writing style is reminiscent of Mary Anne's at times, or perhaps vice-versa.
As an aside, if I were the author, I'd want the head of whoever wrote the cover blurb on the edition I borrowed. It's an entirely inaccurate misrepresentation of what's inside.