Check this great video out! 30 minutes of our very own Tiny and another dev talking about the mechanics of the new BL map in detail. Extra awesome!
http://www.twitch.tv/egx/b/636785081?t=28m
To me, this is pretty OMG. I don't want to say I'm bored with the current borderlands but after 3 years (including pre-release testing) I'm definitely ready to change it up.
Some people will dismiss it as being 'too EOTM' but honestly it feels more 'WAR Black Craig' to me. LOTS of new mechanics to learn, which will reward folks who take the time to learn them and have clever ideas about how to use them. *cough*Fog*cough*
BTW there's a new siege weapon in this video too!
A *little* more detail
This TenTonHammer interview has some more details in it. For example: changes to escorting yaks, complete with a Yak Makeover cheesecake shot.
http://www.tentonhammer.com/interview/guild-wars-2-uncovering-arenanets-new-borderland