It's easy for WoW when you have Chris Metzen voicing 90% of your characters and bosses*.
Also, world quest "voice acting" and the generic lines from NPCs gets old very fast and I'm full glad that most games don't follow suit. I can only hear "GREYMANE'S FORCES HOLD THIS WARDENS TOWER! BREAK THEIR RANKS! SHOW NO MERCY!" so many times before I want to puncture my eardrums.
*Only a mild exaggeration. Chris has voiced a lot of characters and bosses, many of whom are uncredited.
Edit: The one thing I did like was some NPCs getting upset with you if you clicked on them too many times. Like Taoshi, a Pandaren rogue, implying that your body will never be found if you persist in annoying her.
