A great book if you are looking for more information about the many diffrent planets. It offers almost everything you need to know about the noble houses holdings.
However at times someof the discriptions come accross as a little long winded. Also this only realy covers the noble houses and 2 planets controled by the empire. there is almost nothing about league or church worlds here.
But if you want a fully fleshed out world then tis is your book.