Short version for those who don’t want to read the rest of this: It’s a stand-alone so you don’t have to have read the other books and it’s really the best book of the lot, at least until some more get written.
Here’s the relatively spoiler free summary. It’s the story of how Nicholas ends up at a broken down, dying orphanage and how, while having some adventures that show how clever he is, he grows from being a selfish brat to an actually good person.
Seriously, Nicholas starts off as a Brer Rabbit/Anansi archetype and develops into more of an all-loving hero kind of guy. And the book does so in a nice series of beats that does a good job pacing his character arc.
There are two things that I felt made the prequel better than the actual series. Setting/tone and the actual plot.
The main series has a Lemony Snicket Lite feel. An absurd world that has a Kafka-esque set of rules running it. But the reason that works in A Series of Unfortunate Events is because it plays that to the hilt. In The Mysterious Benedict Society, the world seems unfair and absurd but, oh, people aren’t that bad and everything works out.
The Extraordinary et al, the world is still unfair but the tone is much more realistic. And that works much better. Nicholas is a child, albeit, a brilliant one. He has to learn more about the world and people in particular. I’d rather have our son read this version of growing up.
Point number two: despite having scenes of Nicholas tricking bullies and pulling off clever schemes, the plot is really his growth as a person. The riddles and zany conspiracies of the main books are fun but this is more interesting and meaningful.
I almost didn’t read the Extraordinary et al. I enjoyed the series well enough but it wasn’t that special. However the book ended up being a nice surprise.