Neither are 'successors.' They're not trying to be Elder Scrolls games, they're doing their own thing.

Fallout is significantly different from the TES games, so if you're looking for a game with lots of exploration and the ability to create a jack-of-all-trades uber character you'll be disappointed. But if you want to choose your own path through a winding story full of great dialogue and make a character that's very good at one or two things (which usually determines the path you follow), you'll like Fallout.

Man I wanna play Fallout 3 now. I'm not a big Elder Scrolls person.