Just adding back the ability to lie to NPCs would be nice. For example, I would have been so happy to be able to lie in the Chorrol Mages Guild recommendation quest. But instead, once I gave Earana the book she wanted, I go back to Teekeeus and my only option is something along the line of "I did something bad, please punish me.". How about an alternative option like [Lie] "I have spoken with Earana and told her to leave town...and she did.", then Teekeeus tells me "Well done! Here's your recommendation." and I say "Thanks!...you idiot.". Now that would have been fun.
This is huge. One thing I always wanted to do was to "join" the Dark Brotherhood or Thieves' Guild and bring it down from the inside out, bringing information to the guards on the sly.
Instead I had to resort to just slaughtering all the membership and calling it a day.
Whenever you have tow opposing factions, the player should have the option to join either one, or to betray either one, or both... barring extreme circumstances of course.