My son (currently 17 months old) has loved this book since he first layed eyes on it four months ago.
Each animal in this zoo is represented by a baby dressed up in an animal costume. My son first payed attention to the baby faces in the book and has since started pointing to the costumes and the various aspects of the animals that are pointed out in the book. That sounds a bit dull when I write that, but it's really quite fun to watch and listen to him exclaim over moose antlers and crocodile tails. I'm more than happy to read it over and over again for that reason, as well as the fact that I think the pictures are quite cute, too.
If I had to make a complaint it would be that the costumes are sometimes a little more representative than accurate. That is, the peacock is dressed in a brilliant blue all over, which is different from the real bird. But there are other books to teach my son that (as well as real zoos!).
This book is helping him to love books even more as he looks at the faces of the other babies and the costumes they are wearing.