Personally, I'm veeeeery picky when it comes to Voice Acting in Games. In my opinion, it's generally of bad quality and that's mainly for one single reason:
The Voice Actors are told to talk slow, overly pronounced and steady. 
This pisses me off to no end as it takes out all character. I can generally read out a line of dialogue two times before the game even gets close to finishing one sentence. You can neither convey emotions, nor can you build up suspense this way.
"Ruuuuun... foooor... your... lIves... the... wOOOorld... is... coooOOooming... to... an... end... if... we...". BLOODY SKIP ALREADY, ARGHARBL. I don't know, the slow talking pace just kills all the mood for me. Doesn't feel natural. Feels insulting too. Add in generally bad facial animation that makes even the most serious of characters look like they went to clown school and the fact I grew up on subtitles (well, dialogue as written text was the standard in old games

) So ye, I activate it by default and skip large parts of dialogue the second I've read the subtitle.