Based on the trailer, I think
Fallout 3 is sort of like Fable 2, except that it is FPS yet at the same time it is also one of the better Western RPGs with awesome graphics.
Personally, I have only played the original Xbox's
Fallout: Brotherhood of Steel and I didn't find the game to be appealing at all. The only reason why I bought it was that the game only costed 3 bucks. The graphics aren't very good either.