I would like to see missions where you are asked to make some disappear, like they have run away.
So no one is aloud to see the murder, and no one is allowed to find the body. You have to watch your target, wait till they are somewhere alone, and where you can take the body away without encountering anyone. Make sure you don’t leave blood which would rouse suspicions.
This could be done with illusion magic, make people think they have things to do in other places and leave him alone, or hide him with ain invisibility spell to drag the body away without anyone seeing. It could be done with old fashioned stalking, waiting for him to take a walk in a forest on his own accord, or you could befriend the guy ask him to take a walk with you away from the town.
I would like to see an endless stream of assassination quests built from random constraints (a list of things that you must/must not do or things NPC's must/must not notice), and random targets who have just crossed the border (new people so you don’t just kill the entire NPC population of the area).
EDIT:
I like it personally. Here's one that'd be cool.
A lord has challenged another lord to a duel. This other lord is afraid, so you've been hired. Now there are two things. First, nobody can know he was assassinated, so it has to look like an accident. Second, you must make it look like he was going to flee in fear.
So a couple of ways that this could be done. You could sneak into his house and secretly loosen a leg on his chair so that he'd fall and break his neck. You could switch his tea with poison and he'd have 'choked' to death.
Now to make it look like an accident. You could forge a note and put it under his pillow. Or you could loot his safe and put it into his travelling knapsack.
Yay or nay?
I never liked the Oblivion DB quest where you had to kill that person and make it look like an accident (you had to loosen he screws in his wall hanging so it would fall on him) It almost felt like a cheat, I didn’t come up with that, the game presented me with this way to kill him. If I am asked to kill someone and make it look like an accident I want to come up with a way to kill him using the logic and physics of the game itself.
For example I could encourage him to take a walk and bait an animal over to maul him to death, I could get him drunk and ask him to show off by walking on that (tall) wall, I could do a myriad of things if the game logic would allow me. I would much prefer something like this then to be told to loosen a screw, or break a chair leg because I have never broken a chair leg before in the game, or loosened a screw. Performing a task that has not been possible up till this point in the game and will never be done again is a sure fire way for the game to point out its limitations, thus breaking my suspension of disbelief.