Dungeons – At launch there will be 8 dungeons, but don’t fret! This doesn’t mean they’re the same static thing over and over again.Like everything else in the game, ArenaNet is shaking up how dungeons work as well. Every dungeon has a Story mode and an Exploration mode. The Story mode uses concept art and exposition to tell the story similar to the Personal Story. After completing the Story mode of a dungeon, you will unlock Exploration mode. Exploration mode is significantly harder than the Story mode version. Story mode is meant for pretty much any random pick up group, whereas Exploration mode is very difficult content that is meant for a coordinated group of players. Whatever results come of the Story mode version will play out in the Exploration version of the dungeons. Each of the Exploration dungeons have at least 3 paths that the group can vote on that will determine what path they take. The Dynamic Event system is also present in both versions of the dungeons, so even if you play through multiple times, that doesn’t mean you’ll see the same exact thing. Bonus events could spawn from player actions, by location or even at random and change your experience.
But what about the loot you ask?
Every dungeon has its own unique weapon and armor sets. The Story mode has the unique weapons and the Exploration mode has the unique armor sets. When you complete a dungeon you'll be given a token that's used as a currency for either weaopons or armor. So rather than grinding a single dungeon 20 times in hopes that you get what you're looking for, you can just take the token and buy exactly what you want.
Aggro will take into account quite a few factors:
Simple creatures use a system based on proximity, how much damage is being done to them, how much damage they're doing, health of the player, armor, etc. More complex creatures will use all of the above among other things such as using specific skills, attacking the player that is the furthest away from them, focus on players wearing medium or light armor and try to chase them. Some creatures might run away from you, swap weapons to have entirely new skills, dodge your attacks, use specific skills on players at specific times, etc. Different armies will also have their own systems that are based on different themes, skills, and AI.