I don't mind a voiced character as long as they use a decent actor with an awesome voice AND of course as long as my choices are not made for me. Still I think getting an actor for this job to say a few thousand lines would not be very ideal. Just imagine a response to every response from all NPC's in Fallout 3, how that would have been. Not having a voice of a protagonist leaves something mysterious and opens up your imagination, and this essentially is what made previous Fallout games great. Many successful games had no voiced protagonist, games such as Half Life for example.
We don't know very much from the trailer to it's too soon to know if we're getting a voiced protagonist or not. The guy could just be the father of the child you play, or the child itself that just said something during the trailer for the sake of saying anything at all. Or it could be someone from Vault 111 that the protagonist knows, much as how the Lone Wanderer from Vault 101 went after his father, but that would probably not be the case since we've already seen it in a previous title.
Oh and if this is the parent and we're having both male and female characters, they'd have to find someone to voice the mother. This means having two actors for the same job. Just imagine [censored] up on the voice actor, how it would affect the game as a whole. You'd be stuck with this voice of the character you play for the next few dozen hours or so. Much can go wrong, but I have some faith in the ability of the Fallout team on this one. Hopefully they'll do the right thing!