No, I pitch-bend the narration up about 10-15 percent. I like that he has a voice of his own and (sort of) stands as a character separate from me. Also, my normal voice is pretty boring.
Actually, I was pretty impressed with Fallout 3. The decisions weren't nearly so cut-and-dry "Good vs. Evil" decisions as you tend to see in, say, Bioware games. And while a lot of the quest conversations are basically just "Will you help out this old man or ignore him?" scenarios, it really felt like you were free to choose your way in the world. You could handle situations however you wanted, and your choice would lead to consequences, good or bad.
A lot of the choices in the game may still have just been very cleverly-concealed problems, but that's still a step in the right direction.