The Wolves in the Walls is loooong by picture book standards - over 2000 words, when the average is about 700. This is not necessarily a problem if the writing is tight, clear and efficient. If the writing isn't tight, clear and efficient, the length of the book works against you, so that by the end of it, the reader has ended up having a pretty muddy read. It isn't enough that the prose be tight and clear - the story itself can't have any fat, no areas or episodes or moments that don't drive the narrative forward or in some way feed the rhythm of the book. This is where The Wolves in the Walls disappoints.
The basic concept - that a little girl named Lucy hears wolves in the walls and her family doesn't believe her - is awesome, especially because it turns out that Lucy's right. The beginning starts out slowly, but that's not a bad thing as it built up a sort of mild, creepy suspense. But when the slowness continues through the entire of the story it doesn't work so well - there's little sense of disaster when the wolves do come out of the walls, and little sense of climax when the family reclaims their house. The high stakes and suspense are all muffled under cluttered prose and Lucy's overly talkative family. One severe edit would have done the trick, but without it, The Wolves in the Walls is only half of what it could have been.
I find this with a lot of Neil Gaiman's work. He's brilliant and I love the way his brain works and so desperately want to whole-heartedly gobble up everything he writes, but he's undisciplined. The only reason The Wolves in the Walls got published without the edit it deserved is because Neil Gaiman's name would make it sell. If his craft were as developed as his conceptions, he would be amazing, but it rarely is, so I always end up feeling teased by the book's potential. And that's how I feel about The Wolves in the Walls - it's so damn close I could smell the smoke, but no cigar in the end. :(