It was a fantastic book. Garth Nix kept me breathless throughout Sabriel's adventure. There were just the right amount of background information to help the audience understand what went on in the novel, and there were just the right amount of questions left unanswered that will keep readers coming back for book 2. The book can also be read as a standalone, as the main storyline was well wrapped up. 
 However, since I rated The Way of Kings and both entries in Patrick Rothfuss' Kingkiller Chronicles as 5 stars, I felt that Sabriel in comparison falls short in several aspects, as it didn't give me the WOW feeling that i genuinely had with the other books previously mentioned. 
 In terms of world building, Garth Nix could have explained the magical system (the Charter) of the book, better. Right from page one, the author dumped "Charter" on the readers, without really delving in the mechanics of the magical system throughout the book. Readers were left to fend for themselves picking up clues along the way. In a way it works as it avoids a lot of info-dumping. In another way, it does make a lot of things very convenient for the characters as sometimes the characters got out of difficult situations a bit too easily (such as flying the Paperwing) 
 As for the characters, none of the characters stood out except for Mogget. Now that guy is fascinating. The schizophrenia and obvious wisdom makes for a very interesting combination. Sabriel is one strong woman, both mentally and magically. While I do admire her will and focus very much, she did come across as rather plain. No cracking wit, no exceptional insight (though this is probably a result of authorial intention to place the main character in a state of perpetual ignorance), no real flaw etc. She's just, for lack of a better term, meh. 
 I felt the relationship between Sabriel and Touchstone seemed rather rushed towards the end. After Sabriel finding Touchstone irritating for most of the book, the two inexplicably fell in love with each other. Perhaps it was because of the dire situation they found themselves in, you know, like crisis bringing together people. But still, I thought the interaction between them was written in a very cold manner. 
 I have to add that my perception of the book might have been coloured by firstly, speed reading most of the book, hence I may have missed out key details. It honestly is a very fast paced, a lot of things going on kind of story. And secondly, I accidentally discovered, to my great annoyance, that the next book will not feature Sabriel. Regardless of my thoughts towards the character design, I am still invested in her and would honestly want to read about things from her perspective again.