Thunderhead Keep. And Arenanet's been pretty tight-lipped about how the development of GW2 is coming along. A while ago they released a letter, which I can't find at the moment, which basically said the development was going well, even though it was taking a little longer than they had originally expected (I think the initial news release suggested that there would be a public beta in the second half of 2008, but obviously that hasn't happened), and that they don't want to unveil it too early because they want players to be wowed when they finally get it without tons of frustration from glitches that haven't been worked out yet.
So far I know:
-the geography has been slightly messed up because of cataclysmic dragon awakenings
-there are several new playable races, including ones we haven't met yet
-there will be movement in the z-axis in addition to the xy-plane (i.e. jumping, falling, swimming, etc....)
-much of the game will be in the style of a persistent world where you can meet players in the wilderness, but there will still be instanced game play opportunities
-a new form of pvp has been introduced (it sounds very interesting actually)
-Eye of the North's Hall of Monuments will be used to create a legacy between the current game world and the next for linked accounts (name reservations will also operate this way)
err...I probably know more but it's been a while since I've read anything new so I can't remember much.
Personally I'm really excited to hear anything about it. I still enjoy the original game (the best imo), and the original campaign is my favorite of the four (maximum replayability I think). I was really hoping they would at least release some more concept art for players to oggle at in the meantime.
Honestly, Eye of the North was a great expansion campaign. I think they had free trial keys available somewhere online a while back - they may still. I recommend trying it if you can.
Oh, and 420 (was typing the above to Mo when you posted), they've vastly toned down Thunderhead Keep in normal mode. It's not nearly as extraordinarily hard as it used to be. It's still a difficult mission if you don't know what you're doing, but if you pay attention it's doable. Hard Mode is probably on par with what it was on release (I'm also accounting for my inexperience when I first tried it), but it's can be handled with a coordinated team. Meclar and I got slammed with a ridiculous boss spawn, but then we succeeded with another human monk and 5 heroes between the three of us. We actually very nearly didn't survive - it was down to Meclar and the other monk, and Meclar resurrected me and within the next 15 seconds I had most of the party alive again. Unyielding Aura for the win!
So in short - the mission (all of them really) has been balanced out since you guys last tried it. And GW doesn't need the discs. You just need the launcher which you can download from the website.
-Elessar