Yeah, I'm with many of the posters here in that Oblivion is definitly the superior game. Much more vast, colorful, inspired world. Fallout 3's world is depressing, usually pretty dull, and uninspiring. I know that's what they were probably going for, but that doesn't mean I have to like it. That said, I still think Fallout 3 is a great game. Just not near the level of excellence of Oblivion. I also prefer swords and magic to guns and explosives personally.
So I say, even if you DO hate Fallout 3, perhaps at least give Oblivion a chance. Haven't checked amazon for it lately but I'm sure you could get it pretty cheap since it is a relatively old game now. If you do like Fable as you say, you may enjoy at least some aspects of Oblivion, as the atmosphere and things like the magic system seem to be similar. But as I said, expect the core gameplay to be very similar to Fallout 3.