Warning: Long-Winded Rant Below!!
[I can see the voice being done very well. One of the main reasons they decided to add a voice at all seems to be to add some emotion into the world. I'm truly excited to see how it'll be done, and I can already see the game being way better than the previous two, which I still love to death. I know some people find it immersion-breaking to simply hear their character emote a certain way during a certain situation where they certainly would.
The scene of James' death in 3 comes to mind. No matter how much hate welled up inside me towards the Enclave, it didn't translate well into the game. All my character did was stand there, like a hunk of wood. But there's the beauty of it. It's your thoughts. You're free to think however you want, make your character act how you would in whatever situation, and a voice won't stop that from happening. The freedom is still there.
In fact, all of Fallout 3 was kinda like this "predetermined personality" situation. It honestly threw me off, despite it being my favorite entry in the series. Throughout the game, you were free to wreak havoc or be the goody-two-shoes you wanted to be, but it was almost pointless. Through dialogue with James, playing evil, he talks about how he "raised you better than this" or how he doesn't know "what's gotten into you". This honestly sounds like you were a real great kid up until you left the vault. He's surprised by your change in personality, because it's as if your character simply flipped a switch upon leaving the vault. Your character already had a predisposed personality before the game starts.
New Vegas did the complete opposite, having you be this anonymous Courier with an obscure background. You could be who you wanted. Which also wasn't perfect. It left me without any character background. I felt I was playing an even blockier hunk of wood.
Having a predisposed character isn't going to take away any enjoyment had in the previous Beth-entry, because it was already present in that game. Your character had a set background. A kid who was raised by a really stand-up father, to be the most outstanding citizen they could be. If anything, Fallout 4 is going to do this better because all we've seen is that the man/woman has a family, rather than sitting through the character's entire life story and experiences. That short clip has literally almost nothing to do with showing his personality, other than him caring for his family. A perfect mix of vague background and lifestyle check. A platform to build your character off of, if you would.
Plus, who's to say the voice will always have the same personality through every line of dialogue? Nothing is stopping anyone from playing an evil character, and I'm sure the included dialogue would not share the same tone or personality as anything a good character would say.
Sure, you may imagine your character's voice a certain way, but how could that possibly fit in with the already existing pain/power attack clips? Not every voice sounds the same, and neither should those noises. You shouldn't go witch hunting here when the voice situation was never 100% "immersion-friendly" to begin with. I think the whole "Oh, it'll break every bit of enjoyment and immersion for me," is a tad over exaggerating.
We should at least give it a chance. Show support for the best game studio out there. Not many games have gone so far as to do something like this, and we shouldn't make their developers scared to try. So, at least give it a chance before assuming the worst. It's that kind of mindset that makes developers scared to attempt new things in their games, and we shouldn't be the cause of this premature fear.](/spoiler)
Sorry for the rant.
TL;DR - The personality-immersion situation isn't as bad as it seems, it already existed in a sense. We should give it all a chance before burning Bethesda at the stake. Let's not scare away other developers from trying new things.