Well, I loved it, as always.
The thread that has bound the series (TN1-5) together has, obviously, been Thursday Next, but given this, Fforde has not confined himself to a particular formula. The focus to begin with is on SpecOps, and only gradually shifts to the imaginative masterpiece which is Bookworld.
In this book, another bold narrative shift takes place, in that "the" Thursday Next spends most of the book out of the frame, and the first person is now the Thursday Next character within Bookworld - or is it? - who has to see if she can find Thursday Next in time to prevent a genre war from taking place. The distinction is a little arbitrary, of course - the fictional Thursday Next is trying to live up to the reputation of the real Thursday Next - but it does make for different relationships with other characters. (Is the "real" Thursday Next any more "real" than the fictional one?! One of the many fascinating things about Fforde's books is that they raise such complex philosophical questions so playfully.)
The imaginative landscape is reconfigured - Bookworld is redrawn - and a significant number of the characters are the fictional versions of the "real" characters in the earlier book. This may be disappointing for those people who have grown to love them - well, I have too! - but better to stop before they become cliches, or worse, are unable to sustain a further book.
Given the quiet revolution, the story itself is as good as ever - a whodunit/thriller with plenty of red herrings and cliff hangers (hmm, I don't think we've met Cliff in these books yet), a fantasy world which is coherent to surprising depths, a huge amount of fun with language and literature, and everything falling into place only when I thought there was no way it could all be resolved in the number of pages that I had left.
In summary, another outstanding book from Fforde. But as before, come with a clutch to allow your paradigm to shift smoothly ....