Why? One of the aspects of Oblivion I personally did not like was that it drove away from the fantasy element more into a typical middle-ages world. One of the great aspects of Morrowind was that the world was so crazy. The Telavanni towers that required magical means to get up to, the giant mushrooms all throughout the landscape, how it changed from marshland to fields to ashlands, etc.
No, it will still be epic and fantastical, just not crazy fantasy junk.
Here's what I'm thinking (assuming TES V is set in Skyrim): Many natives have been found dead with the same injuries - puncture wounds in their necks (okay, maybe this couldn't've happened in the Middle Ages, but it's more realistic than Oblivion Gates). The leader of the Nord settlement you've been imprisoned in orders your release, and commands you to find and kill any nearby vampires, but not because he thinks you can, but because the jails are full. So he gives you a silver weapon of your choice and sends you on your way. When you come back with vampire dust as proof of your deeds (or maybe you bought some?) he finds how useful you could be. He gives you a task to clear out a camp of bandits. Nothing suspicious, right? Wrong. There's a journal on the body of one of the bandits, and it turns out that they're not even bandits at all - they were nobles on a hunting trip. One was an ambassador from Cyrodiil - this could start a war. When you confront the leader (I'll just say count), he has you arrested for murder, and you are sent off to another prison in said major Nord town.
You have a cell mate, by the name Laven Dreth (if you get the reference: :cookie:). You tell him your story, and he says he has heard a rumor of a secret cult dedicated to eradicating the Nord race. But after he tells you, a block falls out of the wall. Then another. And another. Soon, a person carrying a poisoned dagger walks in through the hole and attacks you! You try to fight back, but the poison paralyzes you. Before the assassin can get in another attack, Laven plays some sweet chin music, and ultimately destroys him. You both escape through the hole. But before you leave town, you have to get a new look, so the guards won't recognize you (enter character creation). You decided to go back to the place where the count was staying. In a remote area you find someone's body - the count's. The REAL count's; the other was an impostor! You ask the steward where the "count" has gone - of course, you'll need to bribe him. He says he dropped a note saying he was going to so-and-so, so you go there, and are jumped by a whole bunch of assassins. You fight them off, and find the count. But this time, he isn't a Nord - he's a dark elf. He was using a disguise to change his face. Lucky he was wearing the same jacket he was at so-and-so castle. You know, the one with the wine stain. You kill him, and find a note describing what his orders were for the so-and-so cult. You have to show this to the leader of the Nords. You try to tell him, but he says he has no time for peasants, as a war between him and the Imperials has just broken out. He says he might consider talking to you if you did him a favor of finding out what happened to so-and-so town. You go there, come back, and tell him it has been destroyed. He thinks it was the Imperials, so he sends an invasion force towards an Imperial town. Little does he know it was the assassins. So he reads the notes, and wants you to destroy the assassins. So you follow some leads, hunt them down, yada yada, but you have to do it asap or else lives could be lost.