The Miserable Mill continues the trend of me liking each book less than the previous one in this series. 
 Don't get me wrong - it's still a fun read with plenty of cleverness and wit, and Celyn still seems to be enjoying me reading her the stories. It's also worth noting that this volume has the lowest average rating on Goodreads of all 13 books in the series, so I'm hopeful things will improve. 
 In this book the established formula is applied with little or no variation. The bad point, for me, though was the descent into truly cartoon writing. In all the books before the world was similar to ours, bizarre, but largely believable. Normal laws of physics applies, things were internally consistent. 
 In The Miserable Mill many things are wholly surreal and/or plain don't make sense. 
 Some random examples: 
 i) The signs being made out of chewed up chewing gum ... why? 
 ii) The Boss having no name and his face being wholly concealed by smoke from his cigar the entire time - that steps into a kind of silly that is very different from the previous books' silliness. I cannot see in my mind a cloud of smoke from a cigar that is totally impenetrable and moves with someone. 
 iii) A log being sawed is moved from its path (where it is held by the fact the circular saw is halfway through its length) by a child with a strip of metal using only the force that can be applied through the adhesion of a piece of chewing gum stuck to both the log and the metal strip. 
 iv) A baby has a lengthy 'sword fight' with a grown and murderous woman. The woman is using a sword and the baby ... is using her teeth. We are repeatedly told that the teeth and sword clash. 
 If the books had begun like this I would be ok with us being in a cartoonish world where that kind of thing happens (though I still wouldn't be able to visualize the sword fight in any satisfactory manner). But the first three books aren't like that (though they do move slowly in that direction) and in book 4 is comes as an unwelcome non sequitur. 
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