His series, The Land of Elyon, is excellent in my humble opinion. In some ways Elyon is what readers have come to expect of fantasy worlds, but it has some unique aspects. I could identify with the choices of the protagonist, Alexa, and enjoyed meeting the other characters as the exciting plots unfolded. There were a few very subtle theological things most readers won't even notice, but they added to the goodness.
Since those books were so good I read another one by the same author called Atherton and didn't like it nearly as well. Intended for older kids, that book is also exciting with well drawn characters and has a very unique fantasy world. However it's the first in a series and I felt completely cheated to discover nothing important had been resolved at the end of the book. Of course every author wants readers to get the next book in a series but I, for one, have no desire to get another one that will probably leave me hanging at the end.
In the Elyon series Carman leaves enough unknown to make us want to read more about the characters and their world, but each book has a complete plot. Atherton doesn't.
Patrick Carman is a gifted writer and I may read more of his work in the future, but probably none in that series.