Personally I felt the story of D4 base game to be a huge let down, especially after all the Lilith hype. It's like they thought just having a dark atmosphere was enough and they needn't bother with an actually interesting plot. Even the ultra cheesy D3 story was better imo, and that's saying a lot. How can you go from such a great story from D2 to ever decreasing quality of D3 and D4, it's perplexing.
Can't wait play it! :)