Whilst a lot of Fallout 3 is going to be different from Oblivion, there are some things that the games will share. A new interview with Gavin "Kathode" Carterat GamesFirst gives some hints (well, one, but it's a slow news day):
GamesFirst!: How have the NPCs been revamped for Oblivion as opposed to Morrowind?
Gavin Carter: Reworking our NPCs is a major focus for us with
Oblivion. Everything about NPCs has been redone from the ground up. For
starters, all of their dialog is fully voiced. Being able to actually
hear the characters speak out loud really adds to the atmosphere. We're
making revisions to how dialog functions in the game as well. Gone are
the encyclopedic database characters of Morrowind who had lists of
generic topics that scrolled off the screen. We're trying hard to give
all NPCs a sense of personality and keeping their topics down to things
that are interesting and unique. The dialog system itself has been
revamped to remove the hyperlink-style keywords sprinkled in among the
dialog. You're now presented with topics and dialog choices in between
NPC dialogs. We find this helps you focus on the information (as
well as our incredible facial animation system) much more, instead of
just hunting through the dialogs for the colored words like in
Morrowind.
It's hardly likely Fallout 3 would have used the pretty terrible dialogue system from Morrowind, so I think the important bit here is the part I highlighted. If Oblivion, with its 100 billion NPCs, is fully voice-acted, it's safe to assume that Fallout 3 with "20 to 40 really deep
strong characters" will be fully voiced as well. If they can get the quality of the voice-overs up to the standard of Bloodlines, I'll be happy.