I can agree that if you hated Oblivion, you probably will dislike Bethesda's Fallout. It makes sense, the ES series is their crown jewel and it's been successful for them, so of course they aren't going to totally abandon their design philosophy for a new title. I'm just very hopeful that they will fix the more glaring issues that Oblivion had.
Really, it's all about the story for me. If they can create an intriguing plot, then I'll be ecstatic. If they can't, then I'll still probably enjoy running around exploring the game world. So I figure I have a high chance of liking Fallout 3, a small chance of loving it, and a minisule chance of hating it. No problem.