A thought: What if, after killling the count, you had to flee through the city? As in, you would spawn right outside the entrance to the keep, and had to run, on foot, out of the gate, with several guards in the way? This would, obviously, be a high-level or late quest, as soloing so many should be difficult. You would also have to flee in a certain time before they managed to close the town gates. This assumes, of course, that an alarm went off.
A nice, specific to vanilla mod (and thus not quite a portable feature to other mods) would be the town (I think Tihr) that has the large count's room with several levels and a winding stairway. You have to make your way down the stairway and kill the count, then escape the room, which then leads you to the scenario above.
And generic bandit missions, rather than just assassination, seems like an excellent idea.