I'm giving a 3 star rating for this book. While I can principally align with the previous commenter on the great characters, I think it's not so perfectly executed in the end.
If you're anywhere near like me, you will probably find the first half of the book really really exciting - a real page turner.
During that first half, you might kind of skip the parts that explain about the Fillory world, because they seem like really irrelevant fillers for the real story that's going on. Besides, the Fillory world very much resembles Narnia, so no credits for the imaginaton of the author in this regard.
So instead of reading the boring Fillory parts in the first half (which are presented as child memories of a book series that the main character had read), you will concentrate on the great characters and what's going on with them.
It came as a surprise to me that the Fillory world becomes very central to the plot later in the book, at which time I had to realize that I had no idea of the whole Fillory story - because I skipped these parts earlier (they are really boring).
The story gets really wild in the second half, but it feels like Alice in Wonderland, just brutal.
Lastly, I think the author hasn't found a satisfying end to the story at all. There's a female character that appears in the end (don't want to spoil it for you), who just doesn't make a lot of sense at this point in the plot, and I cannot imagine how the appearance of this female character could do anything to soothe the main character's pain.
So bottom line for me: it was worth reading, but the first half promised much more than the second half could keep.