The Old Kingdom Trilogy by Garth Nix
This seriously was and still is my favorite young adult fantasy trilogy! I have read it several times. I loved everything about this series, however, I wish each book was a trilogy that focused on the main character, like I would have loved more stories from Sabriel and Lirael. Companion novels are hit and miss, because you really get attached to characters and the next book is new characters!
So it should have been Sabriel 1-3 and then Lirael 1-3 (Abhorsen would have been part of the Lirael trilogy.) Heck Garth could have gave us a series based on each character. Let's say 7 books each? Is that good for everybody? Needless to say, I am a huge Garth Nix fan and love all the books I've read from him so far. It goes without saying that this trilogy gets a huge 5 star rating.
Sorry this isn't much of a review, more of a fangirl over a trilogy I like!
Other Garth Nix Books:
The 7th Tower Series (All 5/5 stars)
The Keys to the Kingdom Series (All 5/5 stars)
I might be biased as I love Garth Nix!
