I love this book. A series of tight little maps drawn old-school style, each one broken out by room/area, so that each section can be revealed to players by what they can see. There are extensive note pages for the DM to use when populating the maps, setting up traps, creatures, treasure, etc.
Look at the hand drawn map, dream a bit, then start filling in and you've got yourself a full complex for a dungeon-crawling campaign!
I'm looking forward to the additional volumes. :)