How apropos. For a book aimed squarely at the young-adult genre's audience, Morgenstern shows a fair bit of linguistic skill. There's a difference between that and good writing ability, though.
First off, the praise. As I mentioned, the writer has a deft touch of the keyboard and can turn a decent phrase. Descriptions are VIVID, colorful, and expansive. I feel like I have a very good grasp on the scenery and the local flavor. The circus itself has a real sense of life and artistry about it.
Sadly, though, that's about where the praise ends for me. This book is, as some say here in Texas, "All hat and no cattle." It walks like a romance, but it doesn't do anything one would associate with one. For instance, the main characters are as flat and lifeless as can be, and they have only the barest and most tenuous connection to the plot itself. Author Fiat is in full effect, as we're left to take on faith that plot events are happening, that characters have the reactions we're told they do, and that we should care one way or the other.
The story as a whole is nonsensical, cruel, and impenetrable. The magic system is a grab-bag of New Rules and New Powers As The Plot Demands, where everything happens off screen, and even when magic is brought out in front of the reader, it simply "is", and the audience in the book is too legendarily thick to recognize that breathing carousel horses and ravens that turn into jackets aren't just slight-of-hand.
If I had to sum this book up in one single word, it would be "Twee", but not just that. Imagine the word set sixty-feet high, in letters carved from ancient granite, except that they're completely hollow inside. The entire book is littered with questionable storytelling choices. The setting constantly flip-flops from time period to time period, forward and back without regard for logical progression. Entire chapters are told in second-person for absolutely no reason whatsoever (which is a choice that should be reserved solely for fanfiction-quality writing), and while not as egregious a sin as second-person, writing in present tense is awfully tetchy for the best of writers.
Long story short, it's a delightful dress. It's flowing, regal, and spectacularly adorned. It's only when you get close that you realize that it's on a dressmaker's dummy and there's not a real person inside.