Fallout 3 was an incredible game with its open world, and provides 100+ hours of gameplay with the expansions. It was fun to play and nearly a perfect RPG with engaging quests and mechanics that worked very well. I came across very few bugs.
I think Skyrim will be an upgrade from Fallout 3 in a different setting, thus GOTY.
I never could get in to Fallout, the post apocalyptic steam punkish thing never really did it for me. High fantasy is totally my thing though.
I logged well over 150 hours in to Oblivion. It's the type of game you can play however you want, the only downside is that there is so much to do that it can feel overwhelming.
Really, check out some of the gameplay videos if you want to be convinced. The combat system looks fantastic, the visuals are stunning. Lore-wise, it's a dream for me because I love Norse mythology and the Nords of Tamriel obviously borrow a lot of their culture from the Viking culture.
In the end, if you played Oblivion and didn't like it, you will not enjoy Skyrim. That's pretty much a given. The game is going to be very similar at it's core. Where it is going to set itself apart is in depth, every system seems to have been improved. That's what is going to set it apart from the Call of Duty rehashes and JRPG clones.