I purchased Dungeonscape on friday, and it has quickly become one of the most fantastic reads I've had. this is not a book that has essential charts and prestige classes to revolutionalize your game. What it does have, is a different way to think about dungeons.
That being said, there are a variety of new traps, including one called an "encounter trap". These traps can bring the entire party into play, not just the overworked rogue. This helps keep things fun. There are a few prestige classes for monsters that make them more appropriate for a dungeon encounter.
The neatest thing, in my opinion, is the encounter planners. I almost disregarded this section, but when I continued to read, I saw how helpful it was. Enemies are broken down by purpose, then it illustrates how to use different monsters with different environments to best effect to create a proper encounter.
It also discusses treating a dungeon like a small city, the npc's found there, conditions, unusual walls, etc.