From the back cover:
Welcome to the Dungeon!
Since the dawn of the Dungeons & Dragons game, the dungeon has remained a place of mystery, excitement, and danger. Purple worms burrow through the earth, eager for their next meal. Savage orcs lurk within the darkness ready to surge forth and lay waste to civilized lands. Strange cults, mutated monsters, and forgotten gods hide within the choking darkness of the dungeon's halls. Nowhere else offers greater prospects for wealth, magic, and power. Yet the horrors that lurk beneath the world never give up their treasures without a fight...
This D&D supplement presents a refreshing new take on dungeon adventures. It shows Dungeon Masters how to inject excitement, innovation and thrilling adventure into their dungeons. new rules for encounter traps allow DMs to build deadly snares to catch the unwary. For players the factotum class is a cunning wanderer, a jack-of-all-trades who can cope with anything the dungeon throws at him. New equipment, feats, and prestige classes give adventures the tools they need to survive beneath earth.
"An Essential Guide to Dungeon Adventuring" - This volume, published relatively late in the 3.5 edition life cycle has a variety of thought, fluff and rules for running dungeon adventures that are interesting and break outside the mold. Authored by Jason Bulmahn and Rich Burlew (creator of Order of the Stick), it remains an interesting reference even aside use of the rules content.
A sample of the writing and tone is this template introduction: "When a dungeon builder needs a deterrent, the only thing better than a giant pit of acid is a giant pit of acid with a shark in it. Until recently, this dream could not be realized because the shark always died after a short time in the acid."