Watched it last night and now I think I understand why it took them so long. It actually seems like they remastered the whole thing for 3D. Textures are amazingly even more crisp now, color is awesome and the 3D effect is pretty excellent. The 3D is not quite enough to take top honors, but it is definitely up there with the best looking ones.
The audio does seem improved over the previous DVD. Oh, and yes, it is still going to give your sub(s) a workout
The mines, the sub on the cliff, and Darla are all quite nice.