TW2 was a fantastic game, but it's extremely different from Skyrim. TW2 is more of a cinematic game. Absolutely beautiful, great combat system, strong story and characters, but it's not much of a role playing game. The story branches, but the gameplay is going to be very linear, there's just replay value. You also don't really choose much about your character. Basically, it's a 20-30 hour game.
It's not a roleplaying game? Sorry, but that's highly amusing. You're playing a role, a "real" person, with a reputation, strengths, weaknesses, likes and dislikes, which directly affect the game. But it's not a roleplaying game?
All previous TES games were almost sandbox games. There's a main quest, which you can ignore for hundreds of hours and not even care. You can be pretty much anything, and do whatever you want at almost any time. We have no idea how strong the plot is, how good the characters are, or how the combat is. But we know it's an Elder Scrolls game, and that's enough to know it will probably be the ultimate RPG of the year.
You can ignore the main quest in Oblivion if you indeed don't care whether anything you do makes any sense at all. But that's hardly roleplaying. And the fact that you can be pretty much anything and do whatever you want also doesn't make it roleplaying. First, because in all regularity, it has no impact on the game whatsoever, so rather than roleplaying, it''s storytelling in your head. Second, an actual person in an actual world can NOT do whatever he/she wants. There are expectations society puts towards them, roles they are expected to fulfill and powers they have to tread lightly around. The Witcher DID pull that off.
Another RPG, Planescape:Torment also gave you a premade character, but left it up to you to go from there. You could turn him into anything from a sadistic torturer into a guilt-ridden lost soul seeking redemption for actions he doesn't even remember committing. You had real choices and they had an effect on the game. And all the time, the game demanded that you consider the philosophical aspects: Is a person responsible for crimes he doesn't remember? Can he truly be someone else than he used to be? Or, as the game put it "What can change the nature of a man?" The answer was up to you. But it had an impact on the story and how people treated you.
In Oblivion, you hardly ever were part of anything. You were the errant boy for Martin Septim. You could stand and watch as he defeated the final foe. You could be Champion of Cyrodiil, but did it give you any privileges except for a nice suit of armour? Hardly. And when you got to be Archmage, you got to be archmage of a mages' guild that had almost ceased to exist. Great job! Heck, even when Sheogorath got you to take over for him, you got his staff and the power to summon Golden Saints etc, but lo, only on the Shivering Isles. Let's not get testy, this guy isn't REALLY part of the club... In essence, you're maneuvering a drone through a world it doesn't belong in.