Dungeon World is a great RPG. I highly recommend it. This book, however, is a little hard to read and get the feel for the system so one point off for that.
It's imperative that you download the free FAQ with this book and read it. It is required reading.
I found the information for the DM to be lacking in this book but there is an excellent book called the Prepless GM that fills in that niche. I highly recommend you get it with this. It's like the missing DM guide for Dungeon World.