I have heard it said the Gordon Freeman is a bad character because he never says anything. The same is said about Chell from Portal, Claude from GTA III, Doom Guy from Doom 3, and most of the other voiceless floating hands that hold our guns for us in first-person games. The silent protagonist is seen as dull. (Because they don't say interesting things.) Or cheap. (Because the game designers don't pay someone to read their dialog.) Or outdated. (Because they're a holdover from the dawn of shooters, before such games had a story, characters, or dialog.) The assumption seems to be that someday we'll get over this silent protagonist business and every game will have a chatty main character who loves to talk about their backstory and has a head full of ideas. I blame this attitude on that most oppressive of all majorities, extroverts.
Personally, I find it really strange to have a voiced protagonist in a first-person game. I can't see my character's face, and I can't see his mouth. (Or, in extremely rare and exotic circumstances: her mouth.) I don't know when he's talking and I don't know what mood he's in. Then suddenly a voice enters the scene. It's supposedly mine, but it's not saying things I want to say and it's not expressing emotions I'm feeling. Why am I inside this guy's head if I'm not privy to what's going on in there?
See, Gordon Freeman isn't an emotionless blob to me. He's a canvas onto which I can project my own thoughts. Asking why he never talks is like asking why he never eats, sleeps, or goes to the bathroom. We can assume he does those things even though they aren't depicted in the game. This lets me decide how I feel and what I think about the world around me. When Gordon Freeman met the half-crazed survivalist priest Father Grigori, I decided I was cautious and disturbed. That's how I felt towards him. The last thing I wanted was for the game designer to bulldoze over my impressions by having Gordon shout, "Yo, Padre! Can you spare a shotgun for a brother in need?"
When the main character speaks, the spectrum of possible audience reactions collapses and the writers tell us outright, YOUR CHARACTER IS ANGRY ABOUT THIS. NOW YOU ARE SAD. NOW YOU ARE TRIUMPHANT. Given the smothering linearity of most modern games and the almost complete abolition of player agency, I really resent the game designer barging into my head and telling me how I'm supposed to be feeling. I'm already trapped in a world where I can't do anything until an NPC screams it at me. I'd appreciate it if I could at least be allowed to form my own thoughts and opinions on it afterward.
Having a voiced protagonist also creates frustrations for me when my character's goals are at odds with my own. In Half-Life 2, when Alyx wants to go rescue her father Eli, the game doesn't have Gordon say why he's helping her. (The game is almost a decade old so I don't want to hear any whining about spoilers here.) Is it because he's in love with Alyx? Because he likes Eli? Because he thinks Eli is crucial to the resistance? Because he wants to kill a ton of Combine forces and this seems like a good excuse? Some of those make sense to me. Some of them strike me as being very wrong or out-of-character. Another player might have a completely different justification for doing the rescue. With voiceless Gordon, we're all free to inject our own reasoning. If the writers told us YOU ARE ONLY DOING THIS BECAUSE YOU'RE IN LOVE WITH ALYX, then for a lot of people Gordon comes off like a dunce who can't see the big picture.
Now, you might want to solve this by giving the player a little dialog tree. Just let them express why they're doing the thing they're doing. That's fine, but with the ability to make choices comes the desire for consequences. Players will get frustrated that the game gives them half a dozen things to say about Eli, and none of them are, "Screw that guy, let's go to the beach." The player will ask, "If my opinion doesn't matter, then why did you ask me?" The expectations created by the dialog tree will pull you away from a linear shooter and towards an Obsidian or BioWare-style RPG. And suddenly you're designing a very different kind of game with different design parameters.
Also, - and I know I complain about this a lot - but your average game writer really isn't up to the task of creating an interesting, deep, and noteworthy protagonist. Adding a voice to the Doom marine won't magically transform him into Lee Everett, Max Payne, JC Denton, or Garet the Thief. More than likely we'll end up with like Chris Redfield, one of the dipshits from Crysis, or a generic Sgt. Whitey McBuzzcut. Having a terrible, annoying, or stupid protagonist is far worse than having a bland one.
The silent protagonist isn't a hack, a shortcut, or a design flaw. It's a perfectly valid and interesting design choice that lets me immerse myself in the world. I've got this one little spot in the gameworld to call my own. The area inside my character's head is mine. Please don't make me share it with a voice actor.