Well, just finished the Dark Brotherhood quest line....I have to say, that is definitely the best quest line yet
It's actually of a reasonable length, unlike the others that feel like they're over before you've begun. It almost feels like the Dark Brotherhood quest line was finished first, and then the others were cut because of development constraints.
I have to question this. The first real mission you have to kill a bandit and optionally kill an old friend. In prior games you could have talked the old friend around and still been rewarded. Not only was there no option to as far as I can tell, but when I talked to the old friends family they thought she was already dead although she was well alive still... just poorly done. It would have been easy to make that better.