This was the best in the series so far. Set entirely in the BookWorld, this novel really lets rip with the imaginative use of language to bend perception of reality. It has the added advantage that the author can draw on classic characters such as Miss Havisham, Heathcliff and Mrs Tiggly-Winkle, which nicely makes up for his weakness in creating and handling his own original characters.
This is just my take on it, but I've had trouble identifying with or liking his original characters, whose motivations seem rather pasted on, the most memorable of all having so far been Bowden, who was actually written as a flat boring person, and Spike, who is a bit of a riff on several stereotypes. Considering that even the original characters in The Well of Lost Plots were more entertaining than in all the preceding series and that these were actually written out as fictional rather than "real" tells you that maybe there is something to stereotypes after all, at least in the context of an adventure sci-fi novel. A plain stereotype is nothing - but mix and contradict it, and you've got something. Thursday herself seems like a character created by the author trying to avoid every single detective cliche: she is not male, lonely, a drunk, or strangely irresistable to the opposite sex, nor does she wear a trenchcoat; and just to contradict the female stereotype to boot, she's not young or beautiful, either. It's hard to build a full character out of negatives, though.
That being said, the books are definitely worth a read for their whimsy and cleverness as well as such fantastic scenes as an audience participation Richard III and shootouts at Wuthering Heights, and this last one well makes up for any faults in the characterisation of the previous novels.