It is readily agreed that the Dark Brotherhood questlines are amongst the finest that The Elder Scrolls has to offer. They often put aside the high-fantasy elements of the world, cut the proverbial crap, and indulge in simple whimsical quests that are executed to resounding success. Instead of pitting you against an evil demon, you have to go kill go kill a bride at her wedding or a mad homeless man.
They are really the perfect example of simplistic game design. They often simply give you a simple objective that under any other circumstances would be boring, and let you tackle it how you want to. More often than not, they represent the more free and immersive quests in the games.
So, it is no wonder that these specific quest-lines are what linger in people's minds long after the games are over. In a world that is incredibly saturated with the same fantasy nonsense, it is incredibly refreshing for a game to indulge base desires and out-there ideas. They really are a testament to good quality quest design, and hopefully every quest in Elder Scrolls VI will have the same polish.
10. The Lonely Wanderer
This is more an investigator quest than an assassin one, and it ultimately serves to place you in the shoes of a proper assassin, hunting down and researching your target so as to ascertain the best possible chance to take care of them.
The quest begins by simply giving you a name. The name of your target to be more precise. You are then forced to ask around, hunt them down and get clues simply through your own decisions. You can search the designated city top-to-bottom or you can find his home and raid his possessions to get the edge.
It is the perfect example of simplicity done well because sometimes, just cutting away the usual game tropes of waypoints and descriptions can create the most memorable experiences. Removing the hand holding allows you be a proper assassin.