I think it was a big change that was needed compared to the first Dead Space. They put Issac in to many situations where it required him to say something to really stick out as a character.
Not to mention.
Giving him a voice is a good approach.
I disagree, I actually love the silent protagonist games, because then you can more easily put yourself in the character's shoes. Some of the best games take that approach, Half-Life, Bioshock (i still thought the story in that game was good despite my feelings for the game overall), Chrono Trigger, Zelda (at least most of them), F.E.A.R, Portal, Fallout etc..
It allows people to use their own judgments and motives when something critical occurs in the game. I know some people hate this style, but I've always been a huge fan of it, and am a little saddened that Dead Space is getting rid of it in the sequel. Still, I'm pretty sure it'll be a great game regardless and I know if done correctly the addition of voice to the main character can add a lot, perhaps even more than the subtlety of a silent protagonist. Let's hope!
It's not that I hate the style, it's just that in some games it can't be pulled off well. Take for instance, the Call of Duty franchise. "RAMIREZ GO UP THAT BUILDING! RAMIREZ SHOOT THAT HELICOPTER! RAMIREZ! MAKE ME A SANDWICH!"
And that's what Dead Space felt like. Isaac go turn on those generators! Isaac! go out into space and kill this giant monster! Isaac, go save your already dead wife! Isaac, go bring me that marker! Everyone in Dead Space does a great job with their acting and lines, but Isaac just comes off as this expendable main character that could be replaced with any other person with the same suit. There is really nothing that makes him stick out (other than the suit).
Giving him character, and the ability to talk, will give him that appeal that's needed. Gordon Freeman doesn't need this because they set up the dialogue and supporting characters so well that the player can easily interpret their reaction. Jack from Bioshock, had an amazing origin behind him that raveled him in mystery, and the story even helped in making him better as a silent protagonist.
Dead Space, is one of those games that needs dialogue for the main character. There isn't much focus on Isaac himself, other than his wife and the Marker helping him. The main attraction, is just the Marker itself.