Hm, I'll have to agree that the story was rather weak. The only real plot development is that apparently the Lucifer guy is still around and Samael did not, in fact, take over hell at the end of Darksiders 1 as it was implied; and that humanity is back. The corruption plot wasn't that bad, I suppose, but it was executed too impersonally. The overall connection to the first Darksiders was reduced too much to references/cameos.
Also, didn't they promise that we would see the other 2 horsemen in this game?
I have strong suspicion that a good deal of the plot was simply put on the chopping block out of time constraints.
The game is more of a prequel than a "sidequel" like they said it would because it pretty much happens entirely between Darksiders tutorial and the first mission.
Oh, also, what's with the massive retcon? Nephalem went from being older than Angels/Demons to being hybrids of Angels/Demons? Another retcon, it seems that Archon was the one who opened the Well of Souls for Abaddon, not Azrael as it was pretty clearly said in the first game?