The world is not static and unchanging – every day is not ‘groundhog’ day. Events occur that can completely change the population of a zone or the population of a group of NPCs within a zone (and the rarer the event, the rarer the rewards -- many exotic items can only be obtained when one of these zone events occur). An example: after you kill some key mobs guarding a hill giant camp, this triggers a zone event that loads up an invading force of Storm Giants who then proceed to attack the Hill Giant camp.
The event system is a big part of the game. We talked a little bit about it on the website, things ranging from Kithicor type stuff to world events to localized events, maybe you clear a path to the hill giant camp and the storm giants decide to invade, but that only happens under certain circumstances, MMO players for a long time having been asking for a more dynamic world, less groundhog day, nobody wants a truly random world or procedurally generated world -- we still want a hand-crafted world but mixing it up and having populations change depending on things that are going on ... it could be a player triggering the event, it could be weather, it could be a certain day (the equinox, what have you) so yes, we're really excited about the event system.
The Event System can actually be summarized pretty easily: Things have a status. Things listen for event triggers. Event triggers can be anything and you could keep adding and adding them. It could be a simple time of day. The thing is a mob of a pretty woman, status non-aggro. It listens for Time of Day triggers. The change of the clock to midnight creates a trigger that the woman becomes aware of. The Event is that when the midnight trigger occurs, the woman transforms into a vampire. It's really a very open system that could be taken very far (and I hope it eventually is).
The goal is Dynamics in a sense -- the content is not always the same and it can change. And again anything that minimizes obvious repetition and the Groundhog Effect plague is generally a good thing.
Smart use would be to start with simple triggers and events, nothing that truly impacts the game or the players, but something that is at least noticeable when you are playing and makes exploring our world a little different and varied.
The slightly more advanced example I've given before (although we've still only scratched the surface) is the Hill Giant/Storm Giant War.
There is a Hill Giant camp in the world, and it is *nasty*. Either even a raid couldn't break into the camp or perhaps we don't allow raids there.
But sometimes the Storm Giants come out of the heavens and attack the Hill Giants. What triggers this? It could be player driven, and could be obvious and simple or very complex, requiring you to have a guildmate on the other side of world who must ring an ancient bell that triggers earthquakes. Sometimes the Hill Giants are forced into disarray because of the earthquake, their guards move inside the gates, the inhabitants are distracted and not watching as vigilantly for an attack. The earthquake happens while you and your friends are watching, hiding from a distance. Sure enough, a Storm Giant army dynamically spawns and heads towards the gates of the Hill Giant fortress. You follow at a safe distance. A huge battle breaks out, giants of both varieties are dying on all sides. What would have been impossible normally (free movement in the Hill Giant region) is now possible. The Hill Giant mobs could change to as they react to the invasion. Certainly the Storm Giant mobs are interesting because they're not normally even spawned.
The adept and clever guild watches for events like this and opportunistically takes advantage of them. In this example they let the two giant clans battle it out, occasionally coming out of hiding a picking off a few mobs that don't normally spawn. Lo and behold, they also spawn with items that are only attainable during this Invasion Event. The game's content changed, rare items were temporarily obtainable, and it made you and your friends pay attention to what was going on in the world.... if you don't have someone, for example, at least occasionally checking to see if the Storm Giants have attacked then you're going to miss it (and the players who pay better attention won't). Or perhaps nobody paid attention, it was off-hours, and the invasion took place but there were no players around to do anything about it.
Regions could be enterable in certain conditions but not in others. NPCs could interact with each other with the result being meaningful to the player. Items can be made very rare but appear more naturally... instead of the valued vambraces only dropping 1 out of 500 times, encouraging players to kill the mob over and over again (boring, repetitive), you could have the trigger for the Storm Giant invasion be just as statistically rare, but since you're following an event and killing the mob that only spawns during the Invasion once, you not only got the desired item but obtaining it was hopefully much more entertaining.