Link is a great example.. I hope they never give him a voice (besides the grunts and yells)
Likewise similar is Samus Aran's case I believe, although in the latest game apparently they changed that...
But if you look at other games such as Morrowind and Oblivion, they have essentially "silent heros"... then again, your hero's have no character really, while Link or Gordon do have
I haven't really played all through the Half-Life series, so I don't know bout Freeman much, but in Link's case, though the guy never really says anything except grunts and yells, there is a lot of body language and facial expressions.. this has traditionally given Link character.. Also the music score helps... for example when link opens his chests and gains new items.. the music conveys some emotions to you, much like his facial expressions..
dunno.. I love mute characters..
Or even the Nameless hero from Gothic.. he certainly isn't mute, but he's got a fairly blank personality that is possible for you to fill in with your own attitudes.. He's a likeable guy on the overall.. and with the gameplay you fill in his character the way you like it.