Now it is well accepted that the Dark Brotherhood is a rather unique faction, more importantly in providing an avenue for evil characters in Oblivion and now Skyrim. While I was happy to participate in a pretty enigmatic group of sociopaths, I feel that the faction storyline could use a more multifaceted approach, one with more player choice. What would I suggest, you ask? Quite simply, a course of action that allows you to directly oppose the Dark Brotherhood. For roleplaying purposes, it would be even more interesting to actually be able to infiltrate the group. The elements of espionage, even murder would still be on the table, albeit in a different scope. To those of you who played through the db, my suggestion should come across as familiar as the presence of a traitor was an underlying current throughout the questline. IMHO, this angle that could really be taken advantage of in the hands of the player.
EDIT: Given the game's late alpha (?) stage, I guess this falls under more of a mod suggestion.