The fact that its made by the same developer as Oblivion and Fallout3.
I've already pre-ordered it because I'm certain I will enjoy it regardless; it's simply disappointing to see a game that is very close to greatness fall short. Oblivion's NPC leveling system was awful: Bandits in daedric armor, enemies that take forever to kill, cougars that were more dangerous than demons. And Fallout 3 threw away one of the most amazing leveling systems ever conceived of for absolutely no reason whatsoever. My marksman had 1 perception, because perception did basically nothing. In fact none of the attributes really did anything except intelligence, strength and agility.
And another problem both of them faced was that it was insanely easy to max out everything, making your character some kind of ubermensch that entirely took me out of the roleplaying aspects of the games. What character did you play in oblivion? You played the exact same kind of character everyone else played. The warrior/mage/archer/thief who was the leader of every single guild in the land. You never alter how you play the game, your experience never really changes unless you mod it. It's not like Fallout 2, where making a new character will drastically change how you experience the game with a witty charismatic pacifist, or a insanely buff but half retarded guy. Hell its not even like Mass Effect 2, where you literally all play as the same dude or dudette, but playing as a vanguard makes the gameplay hugely different from playing as an adept.
But that variety of play and replayability is lacking from all the Bethesda games I've played thus far. I hope that things will be different for skyrim, but I'm not particularly optimistic.