It IS a direct sequel. Yes, it's 200 years later. Yes, it's unlikely to see a single recurring character. Yes, it works as its own standalone game. But it's still a direct sequel to Oblivion in the sense that, without the events of Oblivion, there would be no story. It's all been a big build up to the present story of Skyrim. The jewel of Red Mountain, the Heart of Lorkhan, was "destroyed" and then Martin and his heirs were killed, making the Dragonfires not be lit, thus 2 of the major towers of Tamriel were down, allowing the barriers between Mundus and Oblivion to be weak enough for Dagon to invade. The Oblivion Crisis also plays some sort of significant role in the awakening of the dragons and the coming of Alduin, so says the wall that we've seen in all of the videos for Skyrim.
The details aren't clear, but yes, it's a direct sequel as much as any other game has been a direct sequel.
As much as, but not more than. Without Morrowind, there would be no Oblivion. The Emperor would still have died, but the Barriers, which Red Mountain was helping hold up, would have been strong enough to prevent Dagon's invasion. Same goes for Daggerfall- Numidium was another "tower". And it appears the Staff of Chaos was pretty important too, seeing as how it's on Alduin's Wall.
The plots of each game build on the previous, but the story's are completely self-contained entities. This isn't like Mass Effect, where each game is a part in a trilogy. All games in TES appear to be plots of an overarching storyline, but you don't need to play Oblivion to understand what's going on in Skyrim, which is more than can be said for things like Mass Effect.