Let me start out by saying my fifteen year old, fantasy loving daughter LOVED the Brass Dragon Codex. Read it in two days. Said it was better than other dragon books she'd read recently. To me, that means Rebecca Shelley definitely did something right. And one of the things I believe she did right was she filled her book with action.
In You Can Write Children's Books, Tracey E. Dils advises middle grade books should "rely heavily on visual action . . . One way to ensure you have enough visual action in your plot is to ask yourself if you can think of at least one illustration that can be created for each chapter."
This is advice R. Shelley obviously took to heart. From the get-go. Her first chapter opens with a young dragon discovering his parents have been killed. The next introduces us to two gnomes working with lightning and acid as they try to invent a moving giant. Third, the gnome is burned. The action goes on and on. And so, too, does the reader's interest. I'd definitely recommend this book to young, fantasy loving readers.