i like that he doesn't talk, your own thoughts can be a replacement to Gordons, it's much better than playing a game, being told 'you there, go do the hard stuff while we sit here and drink tea' and having a character go 'yes sir, gladly sir, not a problem sir, OORAH!' when you're thinking 'or maybe you could help this time? no? then go to hell'
the only problem with Gordon's silence is that valve seem to make Alyx Vance talk excessively to cover it up. i spent most of my time in the citadel just wanting to tell her to be quiet.
it's also part of the reason the 'Gordons mind' machinima works so well.