The characters are well-developed and rather fun. I had hoped for a bigger role for Mrs. Pinch, whose habit of losing her spectacles and her exasperated utterance of "Blind me!" made me think that she was more powerful than she seemed. I just wish she had been used more. Nigel has a fascinating backstory which also rings true for the times, and even though I was a little disappointed that Cleona wasn't more of a friend for Grubb, there was a compelling reason for this!
Akin to Stroud's Lockwood and Co., Haberdasher's Knightley Academy or the New-York Circulating Material Repository in Shulman's The Grimm Legacy, the Odditorium is a fascinating venue of magic and mayhem in which readers will gladly lose themselves.
Since fantasy is not my favorite thing, and I find that lists of characters add a daunting quality to a book (thank goodness the list was at the end, not at the beginning with a map-- that usually causes me to run screaming!), I would have preferred that characters such as Mrs. Pinch and Nigel would have had more roles, and fewer characters would have been introduced once the Odditorium took off flying. Also, I'm never fond of main characters suffering from wounds and/or passing out (as in Nielsen's The False Prince and sequels), and Grubb manages to pass out at least three times. Still, I'll definitely be looking forward to the next book!