I loved the Peter and the Starcatchers.
Peter and the Shadow Thieves was even better!
There isn't much I can say about the plot if you haven't read Starcatchers, yet. The book moves and is full of page-turning suspense. I was surprised and delighted at how engaging the book was.
Barry and Pearson have created one of the finest literary villains since Lord Voldemort. Lord Ombra is part Lord Voldemort and part Darth Vader. The authors took all of the despicably evil parts of the aforementioned villains and created a vile, hateful and frightening character. The authors employ a rather slow reveal with the villain, which only serves to make it even juicier.
With the introduction of a more sinister villain, Captain James Hook is relegated more to the animated version of a buffoonish villain. He is still there, but he is no longer the main villain. It seems when Peter became Peter, Hook became the foppish clown that we love so much. This book centers on Peter, Molly, Tink and George Darling. We also learn a lot more about the Starcatchers and what they do.
This book is darker than the first one but it is still not as somber or emotionally jarring as the final Harry Potter books. For people looking for a series to pick up post-Harry, this is a great choice. (I also suggest The Secrets of the Immortal Nicholas Flamel by Michael Scott; it is an impressive and intelligent series.)
You need to give this series a chance. I think you will be pleasantly surprised!