Remember when all they NPC's spoke in text boxes if they spoke at all?  That was a much simpler day, and sometimes still a better option (looking at you Metroid: Other M).  But now with larger storage abilities and greater technologies our characters are coming alive.  They are bringing emotions and urgency to our quests that did not exist before.  I know I am more likely to complete quests a little bit sooner if the NPC actually makes me feel the urgency.  To that we offer our nominees for the best voice acting of 2011:

Star Wars: The Old Republic
Portal 2
Dragon Age 2

And the winner goes to Star Wars: The Old Republic.  This game not only had good voice acting that actually makes you feel for the characters, they have a ton of it.  Every quest has a fully voiced cut scene that you interact in.  It is one of the things that I believe make SWTOR such a compelling game to keep playing.