Flynn hit nail on the head.
To add to what he said. It is written from the perspective of a Kender wizard (edit like what crazy pixie said) in a narative voice as a sort of field guide based on his travels and encounters. The dragon book covered topics like Dragon Anatomy, Combat, Lairs, Society, and Biology (for metallics and chromatics). IIRC all the art was used from previos D&D books like Dracomicon to allow the price to stay low (MSRP $14.95 US for a 64 pg Hard Cover) but the way it is presented is somewhat new with the story attached to it.
The monster book will do the same for things like Kobolds, Orcs, Gnolls, and more iconic D&D monsters like Beholders.
My 4 1/2 YO son also really likes the book.
My ultimate geek dad moment happened a few weeks ago. At the end of a day, I had to go the the 3rd floor of the building (the R&D floor) to get some graph paper. I had already picked my son up from his pre-school so he was with me. All the R&D guys were standing around talking about game design therory, quantum physics, or some other brainy subject. From one end of the hall of designer cubicles my son spots a Gargantuan Red Dragon mini and sprints down the hall yelling "A RED DRAGON, A RED DRAGON". Well he now has everybodies attention so I decide to test his Dragon knowledge on the spot, in front of about a dozen of the R&D team including: Andy Collins, Rodney, Shoe, Mearls, etc. So I ask my son " hey Henry, what is a red dragon's breath weapon?" he yells "FIRE" then I ask "what about a blue" and he replys "LIGHTNING". The nods and smiles from some of D&D's best made me puff out my chest just a little and think to myself "good job Scott your son is a geek"