Well, the clearly laid out lessons include lots of useful vocabulary, grammar structures and answer structures for you to follow along with. The book is colourful which helps to maintain interest and there are particularly useful sections on checking and correcting including common mistakes students make with items like tenses and prepositions. The comprehensive sample answers at the back of the book mean that you always know what a high band score answer looks like which is very important.
Here is the link again for what I believe to be the best IELTS book, click here.