I have to buck the trend here and say Fallout 4. I love Morrowind and Oblivion but the nihilist in me wants to see more desolate and desperate retro-futuristic humanity struggling against the odds, especially with a new game engine and a little more time dedicated to it.
I will never agree with those who say New Vegas is little more than an expansion pack because I feel it is far more than that, but at the end of the day everything just seems so familiar. "Oh look, the door to the secret bunker is exactly the same as the basement door to the Anchorage Memorial!".
I feel the Fallout universe is on a roll at the moment and I just want more more more, as selfish and self-defeating as that may be.