I LOVED this book. I've never read anything like it. If you think (like I did) after reading the blurb that it's a story about a mad scientist, you're wrong. It's about autism. Well, it's not just about that. There is a creepy, dark plot that you might be able to figure out before the main character does, but that won't ruin it for you.
I grew attached to some of the characters in this novel and I'm so upset that Overdrive doesn't have the next book in the series. The Dark Unwinding definitely ends with a cliffhanger and I cannot wait to read A Spark Unseen.
I agree with some other reviewers that it's not very steampunk-ish. There are clockwork toys involved, but that's not the main focus of the story at all. This is more of a creepy Victorian mystery novel.