I think the over the top grimaces is just a way of dealing with the lack of voices... and once again Larian steps in and takes control of your character... like others said, just not focusing the camera on the silent protagonist would have solved it instead of deciding for us how our characters react. The Karlach date was a prime example - why the hell is the camera showing a mute protagonist that I can't controll for 50% of the time? Its boring, its odd and definitely doesn't do anything for my immersion or for the scene itself.
But as 'big' of an issue as it is, its by far not the only one that hinders immersion. The dissonance between tone and story is just represented in this part of the game, but its by far not the worst offender, which remains a combination of factors/disciplines. No facial expression or voice acting can prevent the Dark Urge Gale scene being a bad meme as soon as Shadowheart makes her hand-joke.
