Looks neat. I do wonder how you become a vampire demon thing if you're already a werewolf. Those are vampires, right?
The story is a bit confusing, but it's nice to see an upfront antagonist with presence for once. I feel like the large freeroam RPGs really tend to lack a character who creates a sense of urgency with the plot, though, I understand, too, that with these kinds of games the developers don't WANT a sense of urgency. Perhaps this will be a different experience from the main game, then.
My biggest beef with Shivering Isles was that it was just more of the same game I hadn't had the time to explore a tenth of. I'm down for this if it can give me something that Skyrim itself doesn't (and I do mean more than a demonic transformation--I've technically already got one of those).
EDIT: Thought I should clarify that I don't want a completely different game. What I mean is that I'm hoping to see more urgency with this plot, as it would make it more interesting. I understand that runs counter to the way Elder Scrolls games usually work, but just one add-on with a little more weight to it. I can dream.