I get the idea that if Nintendo doesn't totally nail it with voice acting, fans will bitch. But fans bitched about the Wind Waker's visuals too. If they don't get the motion controls right in Skyward Sword, fans will bitch. This is a risk of changing anything or adding anything to the series and I think that sort of risk just has to be taken at certain points or things will stagnate (which will bring out a different form of bitching.)
Recently, video game anthropologists have recently discovered a
third way to bitch about video game innovation within game series. They found that certain peoples decried the changes to a series, not for ruining the series or for being poor, but that the change did not result into an entirely new IP. Modern anthropologists are puzzled as to the motives of these peoples, as such a position was truly bizarre, even in their times.
By the way, Nintendo has actually used voice acting in an artistic way that added to the game. The EAD team specifically wanted voice in Starfox 64 because it would allow the game to relay information to the player without them having to read the words at the bottom of the screen. (Taking their eye off the action.) And this is possibly why there are so many fond memories of Starfox 64's voice acting. Because in that game, they served the purpose of notification of enemy locations and hints and such.