First, it looks like the entrance for the DLC is around where the hydra in Dark Root Basin is located.
Second, it looks like there is a new forest area with the stone warriors return but with a new weapon.
Third, I'm sure everyone saw the red phantom in the trailer but IGN thought it was just another player but I think it is a new NPC invader because of the sweeping kick.
Fourth, if you notice in the trailer there is a structure that looks like the outside of an arena shown at least twice, could it be Gwyn's boss area in the past. It looks very similiar just an observation.
Fifth and final, at the end of the trailer after the title is shown there is one final shot that if you notice the sword could it be our first look at Artorias in action making his grand entrance for our showdown with him?
Just my observations what do you all think?
http://www.ign.com/videos/2012/05/31/ign-rewind-theater-dark-souls-artorias-of-the-abyss-dlc