Suffice it to say that this book, this entire series, is amazing. Chasing the Prophecy is the perfect ending to this wonderful series.
If you think you don't like middle grade, give it a chance anyway. It's one of the best series, and especially the best endings, I've read in quite some time. There's a great balance of adventure, character development and growth, and sacrifice (Mull handles character death in a spectacular way.)
This is a series that will certainly be moving onto my favorites shelf.