Visually, it remains on the same graphics engine, with a few exceptions ...
In terms of plot, it is (without spoiler) a parallel story, I leave you to discover for yourself, for it is really worth, but we are far from those to which one s awaits when you attack the game, that Death is during the period when War is faced with ardent council.
Nevertheless, there are more big, starting with the PR system that can equip his character with equipment found on the defeated enemies.
There are classical objects, rare objects owned objects (improvable), the mythical object ...
In short, it is a big plus, as it was with War quickly tiresome.
The character of Death is very fast, so it's a pleasure, but for the big brutes, there is the possibility to equip a secondary weapon "heavy" for big damage!
There are more secondary objects and secondary quests, but it is not spoilera on that side!
When extensions (currently 2), they are pretty good, even if "The Tomb of argule" is rather simplistic, the new "The Abyssal Forge" is much longer and interesting.
In short, you will delight in all cases, but do not expect a sequel to Darksiders 1, since it is not one!