This book contains dozens of tables to serve as inspiration for DMs, new and old, to create new dungeons, NPCs, adventurers, quests etc. I have been playing as a DM for more than a year before I decided to get the book, but I still find it very useful for my campaign. It also has plenty of lores for your light reading at night.
To my irritation, however, the book contains appendix for the monsters in Monster Manual which should have been included in MM in the first place. It sorts them according to CRs and environments.
Great guide for the noob that's looking to DM. Probably good for those that are experienced too but I wouldn't know. I'm not one of those. The illustrations are amazing as with all D&D books I've found.