Without giving too much away, a key twist in the original BioShock story is to do with your character being completely mute throughout the game. It was an interesting twist on Gordon Freeman-like character design, and a comment on the game's key themes of determinism versus free will.
In BioShock Infinite, the protagonist - Booker DeWitt - will be able to speak. In an interview with IGN , its creator Ken Levine explained the decision. “How do you go back and say okay, well you're that kind of character again after you already had that discussion with the gamer?” asked Levine. “Our response to it was, let's really place you firmly in the world this time. Let's give you a story, let's give you a character to develop a personal story...You're very active, your story is very active, Elizabeth's story is very active.”
Although the protagonist may have found his vocal chords, Levine still values the use of silence in the game. Core to the game is damsel-in-distress Elizabeth's relationship with Songbird, a strange mechanical bird that's served as her friend and warden, and is now pursuing Elizabeth and DeWitt through the airborne city of Columbia. But, as Levine says, Songbird will never utter a word.
“The nice thing about silence is it forces you to make very clear decisions about that character,” said Levine. “It forces you to make that character have very clear motivations because you can't [get] caught up in a ton of subtlety...It doesn't necessarily require words.”
Levine goes on to point out that visuals are more important than sounds in-game, because you generally tend to only hear a line of dialogue once, whereas images stay on screen for a lot longer. And the BioShock games have always been great at this visual storytelling - watch the original's intro without sound and you still get a fairly good idea of what's going on.
It's an interesting change to the franchise. Adding vocals to Isaac Clarke in Dead Space 2 was a vast improvement, and his character suddenly felt a lot more fleshed-out - so to speak. But the critical question is how the story's going to work in its inevitable twists without having a protagonist who gasps “OH MY GOD I REALLY WASN'T EXPECTING THAT DID YOU JUST SEE WHAT HAPPENED” all the time.