Zerging is always an issue for open world content where anyone can participate, Devs tend to build encounters based on a minimum player standard, ie a player will have at least x amount of gear, skill, experience. But when you have a lot of players many of those players have more than the required minimum and so it becomes a zerg. This is why instancing works so well, you can limit the number of participants and you can create tiers of content and keep increasing the minimum requirements for each successive tier to keep it challenging and not a zerg.
Don't get me wrong I want GW2 to be awesome, I've browsed through a lot of this thread and the official site and watched a ton of videos this last few weeks, I really like the look of the world, the skill system, even the outdoor stuff.
But I remain unconvinced about the endgame, and so I will play devils advocate until someone convinces me that what Arenanet are doing will work.
---------- Post added 2011-09-20 at 12:47 AM ----------
In WoW I raided, and every once in a while I would get the urge to PvP. But that only provided a limited amount of entertainment after TBC, raids were made far more accessible (easier) and so took less time. I also despise the new normal/hardmode system, since I view it as the same content twice. This to me was the reason I quit WoW, I spent far too much time sat about waiting for raids, and of late there has been precious little raid content.
It's also the reason I currently play RIFT. There have been 23 raid bosses added in the last six months, there are lot's of open world invasions and raids, exploration is meaningful via collectable artifacts, achievements and rare spawns, there is real world PvP (and lots of it), and shortly we will have alternate advancement and 1-2man content. The content is varied and thick and fast, it's WoW on amphetamines.
I think part of my problem is that I am more a hardcore gamer, I game for the challenge, to be competitive. MMO developers have realised that the vast majority of MMO gamers are no longer the geeky dedicated few but the casual everyday guys, and are catering to them. You just have to look at the number of new dungeons this expansion compared to any other in WoW and the nerfs to older raid tiers to see that.
And yes, I am a geek