This anthology has a host of great authors and while I'm glad I bought it, it was clearly not the best effort for some of them. These are only my opinions and everyone's views are different but a few examples of my reactions to the stories are below to help clarify my opinion of the anthology.
I thought 'The Duel' by Lev Grossman was wonderful. It added some color to characters from 'The Magicians' and was an enjoyable story from start to finish. Just my two cents, by Mr. Grossman's story alone makes the anthology a worthwhile purchase. In my opinion, this was the best example of the stories I thought of as 'very good' in this anthology.
An example of what I term an 'okay' story for this anthology is 'The Martyr of the Roses' by Jacqueline Carey. It's a well written tale with an interesting premise, but the story and its characters never drew me in. All in all, it's a solid story, but just not my thing.
Unfortunately, there were a couple of tales I found truly awful. I'll just pick on one as an example, and I'll add the caveat that I bought the audiobook version of this anthology so it's always possible that the reading itself damaged the story. With that said, I couldn't stand 'How Old Holly Came to Be' by Patrick Rothfuss. Full disclosure: I am a fan of Mr. Rothfuss' Kingkiller Chronicles--I have both HB and PB copies of those two books and am impatiently awaiting the third. Regardless, I found the story to be trite, unentertaining, and frankly a little too impressed with itself. While listening to the story, I felt like someone was yelling at me, "Look at me! Aren't my little techniques cool! Hey! A tree is the main character. Did you hear me?! I said a tree! How awesome am I that I can write about a tree!" While I'm overstating that a bit, I started off by listening to Mr. Rothfuss' story first and nearly threw away the anthology b/c the story annoyed me so much. As with all things, your mileage may vary. Hopefully, it does for this story.