I've loved this series from the start. This is the final book in the series, and as such it answers all the questions about the black crystal that has been plaguing the protagonists since the first or second book. I generally enjoyed this book, although as it got closer to the end, a lot of action was packed into few pages. And I'm still not sure I quite *got* everything (I'll have to go back and reread)
The ending? I won't spoil it, but let's just say I'm torn. I like certain aspects of the ending, others seem too...hm, saying anything more would be a spoiler.
I do recommend this book. It's a must read if you've been following the series.