With a silent protagonist, dialog can become both more and less involving. This would all come down to the writing, leaving the writers responsable for creating witty, touching, gritty, or whatever kind of dialog for your character..
With a voiced PC, responsabilities for good dialog appear on multiple levels. Writers have to come up with good story, actors have to devlop character voices, sound teams have to edit the recordings, artists have to sync up the sound to the animations, programmers have to time everything and debug any issues. Standard opperation procedure for any game, but you can see multiple spots where issues could happen. Just a thought.