This book is absolutely phenomenal.
The descriptions are excellent. The character development is fantastic. The depth of each person in the text is truly amazing.
While the book starts out a bit slow as it introduces the many, many characters that come alive in its pages, it picks up fairly quickly and will leave you wondering, "How did I love a book so much that contains a cast of some of the most awful people?" Rowling has such an amazing talent for writing. I love the ways she tries all the ends together and creates multiple storylines.
Disclaimer: If you're reading this book solely because Rowling wrote Harry Potter, then you're reading it for the wrong reason. This book has no ties to the wizarding world and is completely different. So don't think about Harry Potter at all while reading it. Just enjoy if for the piece of perfection that it is all on its own.